Image sensing apparatus

ABSTRACT

A camera includes a focus-detection module  130  inserted into or withdrawn from an optical path between an image-sensing optical system ( 152-155 ) and a CCD image-sensing device ( 111 ). An image pick-up signal from the CCD image sensing device ( 111 ) is used as ordinary image data for recording when the module ( 130 ) is withdrawn from the optical path and as image data for rangefinding when the module ( 130 ) is inserted into the optical path. The focus-detection module ( 130 ) is internally provided with first through fourth mirrors ( 131, 132, 133, 134 ), a field lens ( 135 ) provided between the second and third mirrors and secondary image forming lenses ( 137 ) provided between the third and fourth mirrors, whereby two secondary images are formed on the CCD image sensing device ( 111 ). The two secondary images are used for rangefinding or focusing.

BACKGROUND OF THE INVENTION

This invention relates to an image sensing apparatus having an automaticfocusing function for focusing the image of a subject.

So-called digital still cameras photoelectrically convert the image ofan object, which has been formed by an image sensing optical system, asa still image using an image sensing device, and record the convertedimage in a memory or the like. Focus detection devices for automaticfocusing used in such digital still cameras usually rely upon one of thefollowing four methods:

(1) TTL (Through The Lens) secondary image forming phase-differencedetection: Optical images that have been formed by passage throughdifferent pupil areas of an image sensing optical system are formedagain as a pair of secondary images on a focus detection lens via asecondary image forming optical system and the state of focus of theimage sensing optical system is detected from the spacing between thetwo secondary images.

(2) Passive triangulation: Two images of an object are formed on a focusdetection sensor by two optical systems spaced apart by a predeterminedbaselength, and absolute distance to the object is sensed from thespacing between the two images formed.

(3) Active triangulation: A rangefinding pattern formed on an object bya light projection system is received by light-receiving systems spacedapart by a predetermined baselength, and the absolute distance to theobject is sensed based upon outputs from the light-receiving systems.

(4) Hill-climbing sharpness detection: Part of an image sensing opticalsystem, or the image sensing device, is oscillated minutely along thedirection of the optic axis and the state of focus of the image sensingoptical system is detected from the degree of fluctuation ofhigh-frequency components (which are in synchronization with theoscillation) of the object image formed on the image sensing device.

The following finders are used as monitors for verifying thephotographic area of the above-mentioned digital still cameras:

(a) an optical TTL finder, which allows the photographer to view theimage of the object formed by the image sensing optical system;

(b) an optical rangefinder, which allows the photographer to view animage formed by a finder optical system that is different from the imagesensing optical system; and

(c) a photoelectric finder whereby an output obtained byphotoelectrically converting the image of an object is displayed on amonitor, such as an a liquid crystal display.

The prior art described has a number of shortcomings, which will now beset forth.

The secondary image forming phase-difference detection method and thepassive triangulation method require the use of a photoelectricconverting sensor for focus detection in addition to the image sensingdevice for acquisition of the photographic image. This raises the costof the focus detection mechanism and increases the size of the imagesensing device.

With the passive triangulation method and the active triangulationmethod, the focal length and baselength of the rangefinding opticalsystem cannot be made very large. As a result, it is required that thedimensional precision of the component parts be very high in order toassure measurement accuracy.

The active triangulation method, besides having the drawback set forthabove, requires a special-purpose light receiving device for receivingprojected light. This raises the cost of the focus detection mechanism.

With the hill-climbing sharpness detection method, the in-focus positioncannot be detected instantaneously when the object is greatly out offocus. Though this is not a major obstacle in a movie camera, it doesmake a digital still camera difficult to use and can result in lostphoto opportunities.

The conventional finders have the following drawbacks:

The optical TTL finder requires a, such as quick-return mirror orhalf-mirror, for separating and switching between a photographic lightflux and a finder light flux. This results in an apparatus of largesize.

The optical rangefinder uses a double-image coincidence mechanism inorder to display the state of focusing. The result is a complex, costlystructure.

The photoelectric finder displays images at a low resolution and makesit difficult to confirm the state of focusing accurately.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an imagesensing apparatus that is capable of performing autofocusing highlyaccurately through a simple structure.

According to the present invention, the foregoing object is attained byproviding an image sensing apparatus comprising photoelectric conversionmeans for photoelectrically converting an image of an object obtainedthrough image forming optics; optical path changeover means provided onan optical path between the image forming optics and the photoelectricconversion means and movable between first and second positions forchanging over the optical path in such a manner that a first image ofthe object is formed on the photoelectric conversion means when theoptical path changeover means is at the first position and a secondimage of the object is formed on the photoelectric conversion means whenthe optical path changeover means is at the second position; focusdetection means for detecting the state of focus of the image formingoptics using the first image when the optical path changeover means isat the first position; and image sensing means for picking up the secondimage using the photoelectric conversion means when the optical pathchangeover means is at the second position.

In accordance with this image sensing apparatus, focus detection andimage pick-up can be performed by a single photoelectric conversionmeans. As a result, it is unnecessary to separately provide costlyphotoelectric conversion means for focus detection, thus making itpossible to provide a small-size, inexpensive image sensing apparatus.In addition, a low-resolution image for focusing and a high-qualityimage for photography can be obtained using the same image formingoptical system. Specifically, the apparatus utilizes an image formingoptical system for image pick-up and the photoelectric conversion meansthereof effectively to make possible rangefinding by TTL secondary imagephase-difference detection or passive triangulation. As a result, it isunnecessary to separately provide costly photoelectric conversion meansfor focus detection, thus making it possible to provide a small-size,inexpensive image sensing apparatus capable of highly accuraterangefinding through a simple structure.

According to a preferred aspect of the present invention, the opticalpath changeover means of the image sensing apparatus has focus detectionoptics for forming two secondary images as the second image of theobject from a pair of light fluxes obtained by passing the image of theobject through different pupil areas; the apparatus further comprisingmeans for detecting a phase difference between the two secondary images,which have been formed on the photoelectric conversion means, when theoptical path changeover means is at the first position.

As a result, the state of focus of the image forming optical system isdetected by TTL secondary image forming phase-difference detection. Thismakes it possible to perform accurate detection of focusing in a shortperiod of time even in a case where the object is greatly out of focus.

According to a preferred aspect of the present invention, the opticalpath changeover means of the image sensing apparatus includes: a firstmirror for deflecting an image forming light flux in a directiondifferent from an image forming optic axis connecting the image formingoptics and the photoelectric conversion means; and a second mirror forreturning the deflected light flux to the image forming optic axis.

As a result, a focus detection optical system having a prescribedoptical path can be accommodated in a small space, thus making itpossible to reduce the size of the image sensing apparatus.

According to a preferred aspect of the present invention, the opticalpath changeover means of the image sensing apparatus includes a beamsplitter for splitting an image forming light flux into light fluxes infirst and second directions at a predetermined ratio of lightquantities; the apparatus having finder means for viewing the image ofthe object along the second direction.

The photographic area of the field and the state of focus of the objectcan be confirmed visually in an accurate fashion by a TTL opticalfinder. This makes it possible to prevent failures when taking pictures.

According to a preferred aspect of the present invention, the opticalpath changeover means of the image sensing apparatus has lens means formaking the image forming power of the image forming optics different atthe first and second positions.

As a result, a focus detection optical system having a prescribedoptical path can be accommodated in a small space, thus making itpossible to reduce the size of the image sensing apparatus and to obtaina wide range of focus detection.

According to a preferred aspect of the present invention, the imagesensing apparatus further comprises release operating means, wherein thefocus detection means is activated in response to a first operation ofthe release operating means, and the optical path changeover means isswitched from the first position to the second position in response to asecond operation of the release operating means.

As a result, the transition from a focus detection operation to an imagepick-up operation can be achieved quickly, thereby making it possible toperform focusing and image pick-up operations in a short period of timeand to prevent the loss of photo opportunities.

According to a preferred aspect of the present invention, the imagesensing apparatus further comprises display means for displaying thefirst image of the object when focus detection is performed by the focusdetection means and the second image of the object when pick-up isperformed by the image sensing means.

As a result, the state of focus of an object undergoing focus detectionand the image of the object at the time of image pick-up can beconfirmed visually in the form of an electronic image even if there isno optical finder provided. This makes it possible to prevent failureswhen taking pictures.

According to a preferred aspect of the present invention, the imagesensing apparatus further comprises focusing control means forperforming focusing based upon the results of focus detection by thefocus detection means.

As a result, TTL focus detection is performed with a coarse imageprojected before image pick-up, and automatic focusing is carried outhighly accurately in a short period based upon the result, therebymaking it possible to focus the image of the object. A high-definition,focused image can subsequently be acquired.

According to a preferred aspect of the present invention, the imagesensing apparatus further comprises display means for selectivelydisplaying the first and second images of the object; wherein theoptical path changeover means has image magnification changing means forforming the first image on the photoelectric conversion means at a firstmagnification at the first position and forming the second image on thephotoelectric conversion means at a second magnification at the secondposition, whereby sizes of the first and second images displayed on thedisplay means are made substantially the same.

In accordance with this arrangement, the normal image of an object andthe reduced image of the object obtained by projection can be displayedwith their sizes equalized in regard to the same subject imaged atdifferent optical characteristics. This improves the ability to visuallyconfirm an image of reduced size.

According to a preferred aspect of the present invention, the opticalpath changeover means of the image sensing apparatus forms a pluralityof images of the object on the photoelectric conversion means at thefirst position and forms a single image of the object on thephotoelectric conversion means at the second position.

In accordance with this arrangement, both an image for focus detectionand an image for photography can be obtained through a simple structureby a single image sensing means.

According to a preferred aspect of the present invention, the opticalpath changeover means of the image sensing apparatus forms the firstimage of the object at a location displaced from the center of alight-receiving portion of the photoelectric conversion means at thefirst position and forms the second image of the object at the center ofthe light-receiving portion of the photoelectric conversion means at thesecond position.

In accordance with this arrangement, only a small image signal that hasbeen formed on part of the light-receiving area of photoelectricconversion means is read out in a short period of time to acquire thefirst image of the object, and the entire image signal of thelight-receiving area of the photoelectric conversion means is read outto acquire the second image of the subject.

According to a preferred aspect of the present invention, the secondoptical image forming means of the image sensing apparatus has an imageforming power different from that of the first optical image formingmeans.

As a result, rangefinding based upon passive triangulation can becarried out.

According to a preferred aspect of the present invention, the imagesensing apparatus further comprises image signal recording means forrecording the output of the first photoelectric conversion means.

As a result, an image obtained from an image forming optical system forphotography and an image obtained from the photoelectric conversionmeans thereof can be recorded and preserved.

According to a preferred aspect of the present invention, the firstoptical image forming means of the image sensing apparatus includes azoom lens and the rangefinding means has image magnification correctionmeans for correcting a fluctuation in image magnification thataccompanies a zooming operation of the zoom lens.

This arrangement is such that when the image forming optical means forimage pick-up is used for rangefinding, a parameter correctionconforming to the power fluctuation is carried out to perform arangefinding calculation. This makes it possible to perform accuraterangefinding at all times even when power fluctuates.

According to a preferred aspect of the present invention, the imagesensing apparatus further comprises display means for displaying thefirst image.

In accordance with this arrangement, the image of a subject for imagepick-up is displayed for monitoring. As a result, the state of subjectfocus can be checked and it is possible to prevent the taking of aphotograph that is out of focus.

An image sensing apparatus according to a preferred aspect of thepresent invention comprises projection means for projecting arangefinding a light flux toward an object to form a rangefindingpattern on the object; optical image forming means, which is spaced awayfrom the projection means by a predetermined baselength, for selectivelyforming the image of the rangefinding pattern and the image of theobject; photoelectric conversion means for photoelectrically convertingthe image of the rangefinding pattern and the image of the object; andrangefinding means for sensing the distance between the optical imageforming means and the object based upon an output from the photoelectricconversion means when the image of the rangefinding pattern has beenreceived by the photoelectric conversion means.

In accordance with this arrangement, both a projection pattern forrangefinding in active triangulation and an image of the object can beacquired by a single image sensing system, as a result of which theapparatus can be reduced in size and lowered in cost.

According to a preferred aspect of the present invention, the opticalimage forming means of the image sensing apparatus includes a zoom lensand the rangefinding means has image magnification correction means forcorrecting a fluctuation in image magnification that accompanies azooming operation of the zoom lens.

In accordance with this arrangement, when the optical image formingmeans for image pick-up is used for rangefinding, a parameter correctionconforming to the power fluctuation, is carried out to perform arangefinding calculation. This makes it possible to perform accuraterangefinding at all times even when power fluctuates.

According to a preferred aspect of the present invention, the imagesensing apparatus further comprises image signal recording means forrecording the output of the photoelectric conversion means when theimage of the subject has been received by the photoelectric conversionmeans.

As a result, an image obtained from an image forming optical system forimage pick-up and an image obtained from the photoelectric conversionmeans thereof can be recorded and preserved.

According to a preferred aspect of the present invention, the imagesensing apparatus further comprises wavelength region selecting means,which is interposed between the optical image forming means and thephotoelectric conversion means, for passing a first wavelength regionwhen the image of the rangefinding pattern is photoelectricallyconverted and passing a second wavelength region when the image of theobject is photoelectrically converted.

In accordance with this arrangement, a wavelength selection suited toacquisition of a pattern image for rangefinding is performed at the timeof rangefinding and a wavelength selection suited to acquisition of theimage of the object at the time of image pick-up. As a result, highlyaccurate rangefinding can be performed and it is possible to obtain ahighly precise image that is free of unnecessary light rays.

According to a preferred aspect of the present invention, the imagesensing apparatus further comprises focusing means for focusing thefirst optical image forming means based upon an output of therangefinding means; focal shift discrimination means for discriminatingthe state of focus of the image of the object based upon outputs fromthe rangefinding means and the focusing means; image signal combiningmeans for combining outputs from the first and second photoelectricconversion means; display means for displaying an output image from theimage signal combining means; and combining control means for changingthe operation of the image signal combining means based upon an outputfrom the focal shift discrimination means.

In accordance with this arrangement, the extent to which the image of anobject is out of focus can be checked visually and clearly by imagescombined and displayed. This makes it possible to prevent the taking ofa photograph that is out of focus.

According to a preferred aspect of the present invention, the combiningcontrol means of the image sensing apparatus varies relative amount ofoffset between display positions, on the display means, of outputs fromthe first and second photoelectric conversion means in dependence upon afocal shift signal output by the focal shift discriminating means.

In accordance with this arrangement, the amount of focal shift of theimage of an object can be checked visually and clearly from the amountof relative offset between two images displayed in superposition. Thismakes it possible to prevent the taking of a photograph that is out offocus.

An image sensing apparatus according to a preferred aspect of thepresent invention comprises optical image forming means for capturing alight flux from an object and forming an image of the object;photoelectric conversion means for photoelectrically converting theimage of the object; rangefinding means for sensing the distance betweenthe optical image forming means and the object; focusing means forfocusing the image forming optical means based upon an output from therangefinding means; display means for displaying the image of the objectfrom the photoelectric conversion means; focal shift discriminationmeans for discriminating the state of focus of the image of the objectbased upon outputs from the rangefinding means and the focusing means;and display control means for varying the form of display of the imageof the object on the display means based upon an output from the focalshift discrimination means.

In accordance with this arrangement, the amount of focal shift of theimage of an object can be checked visually and clearly based upon imagescombined and displayed. This makes it possible to prevent the taking ofa photograph that is out of focus.

According to a preferred aspect of the present invention, the displaymeans of the image sensing apparatus has first and second display areas,and the display control means varies the position of a displayed imagein the second display area relative to a displayed image in the firstdisplay area in dependence upon a focal shift signal from the focalshift discrimination means.

In accordance with this arrangement, the amount of focal shift of theimage of an object can be checked visually and clearly from the amountof relative offset between two images displayed in superposition. Thismakes it possible to prevent the taking of a photograph that is out offocus.

According to a preferred aspect of the present invention, the focalshift discrimination means of the image sensing apparatus detects theamount of focal shift from outputs from the rangefinding means and thefocusing means.

As a result, a finder display or the like can be presented usinginformation relating to the amount of focal shift sensed. This makes itpossible to prevent the taking of a photograph that is out of focus.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the construction of an imagesensing apparatus according to a first embodiment of the presentinvention, this diagram showing the apparatus at the time of focusdetection;

FIG. 2 is a diagram showing the formation of images of an object whenthe object is in focus at the time of focus detection according to thefirst embodiment;

FIG. 3 is a diagram showing the formation of the images of an objectwhen the object is not in focus at the time of focus detection accordingto the first embodiment;

FIG. 4 is a diagram showing the image sensing apparatus at the time ofimage pick-up according to the first embodiment;

FIG. 5 is a diagram showing the formation of the image of an object atthe time of image pick-up according to the first embodiment;

FIG. 6 is a flowchart showing a procedure for controlling a cameraaccording to the first embodiment;

FIG. 7 is a flowchart showing a procedure for controlling a lensaccording to the first embodiment;

FIG. 8 is a diagram illustrating part of a focus detection opticalsystem according to a second embodiment of the present invention;

FIG. 9 is a diagram showing the formation of the images of an objectwhen the object is in focus at the time of focus detection according tothe second embodiment;

FIG. 10 is a diagram illustrating part of a focus detection opticalsystem according to a third embodiment of the present invention;

FIG. 11 is a diagram showing the formation of the images of an objectwhen the object is in focus at the time of focus detection according tothe third embodiment;

FIG. 12 is a block diagram illustrating the construction of an imagesensing apparatus according to a fourth embodiment of the presentinvention, this diagram showing the apparatus at the time of focusdetection;

FIG. 13 is a diagram showing the formation of the images of an objectwhen the object is in focus at the time of focus detection according tothe fourth embodiment;

FIG. 14 is a diagram useful in describing the state of a display on adisplay unit at the time of focus detection according to the fourthembodiment;

FIG. 15 is a diagram showing the image sensing apparatus at the time ofimage pick-up according to the fourth embodiment;

FIG. 16 is a diagram showing the formation of the image of an object atthe time of image pick-up according to the fourth embodiment;

FIG. 17 is a flowchart showing a procedure for controlling a cameraaccording to the fourth embodiment;

FIG. 18 is a block diagram illustrating the construction of an imagesensing apparatus according to a fifth embodiment of the presentinvention, this diagram showing the apparatus at the time of focusdetection;

FIG. 19 is a diagram showing the construction of an image sensingapparatus at the time of image pick-up according to the fifthembodiment;

FIG. 20 is a block diagram illustrating the construction of an imagesensing apparatus according to a sixth embodiment of the presentinvention;

FIGS. 21A, 21B are diagrams useful in describing the state of imageformation when rangefinding is performed according to the sixthembodiment;

FIGS. 22A, 22B are diagrams useful in describing the principle ofimage-magnification correction according to the sixth embodiment;

FIG. 23 is a diagram useful in describing the concept of an image signalwhen a rangefinding calculation is performed according to the sixthembodiment;

FIG. 24 is a flowchart showing a procedure for controlling an imagesensing apparatus according to the sixth embodiment;

FIG. 25 is a diagram showing the construction of an image sensingapparatus at the time of rangefinding according to the seventhembodiment;

FIG. 26 is a diagram useful in describing the state of formation of aspot image for rangefinding according to the seventh embodiment;

FIG. 27 is a diagram useful in describing the concept of an image signalwhen a rangefinding calculation is performed according to the seventhembodiment;

FIG. 28 is a diagram showing the construction of an image sensingapparatus at the time of image pick-up according to the seventhembodiment;

FIGS. 29 is a diagram useful in describing the state of image formationwhen image pick-up is performed according to the seventh embodiment;

FIG. 30 is a diagram useful in describing the state of an image displayafter image pick-up according to the seventh embodiment;

FIG. 31 is a flowchart showing a procedure for controlling an imagesensing apparatus according to the seventh embodiment;

FIG. 32 is a block diagram illustrating the construction of an imagesensing apparatus according to an eighth embodiment of the presentinvention;

FIG. 33 is a diagram useful in describing the concept of an image signalwhen a rangefinding calculation is performed according to the eighthembodiment;

FIG. 34 is a diagram useful in describing the state of an image displaywhen rangefinding is performed according to the eighth embodiment;

FIG. 35 is a flowchart showing a procedure for controlling an imagesensing apparatus according to the eighth embodiment;

FIG. 36 is a block diagram illustrating the construction of an imagesensing apparatus according to a ninth embodiment of the presentinvention;

FIG. 37 is a diagram useful in describing the state of image formationwhen rangefinding is performed according to the ninth embodiment;

FIG. 38 is a diagram useful in describing the state of an image displaywhen rangefinding is performed according to the ninth embodiment; and

FIG. 39 is a flowchart showing a procedure for controlling an imagesensing apparatus according to the ninth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to the drawings.

<First Embodiment>

FIGS. 1 through 7 are diagrams relating to a first embodiment of thepresent invention.

FIG. 1 is a block diagram showing the construction of an image sensingapparatus according to a first embodiment. This embodiment relates to aso-called single-lens reflex camera in which an interchangeable lenshaving an image sensing optical system is capable of being removablymounted on a camera body having a image sensing device.

The camera includes a camera body 101 having a mount (not shown) joiningvarious functional portions for image pick-up and an interchangeablelens 151, described later. An object is indicated at OBJ.

The camera is internally provided with a single-chip microcomputer 102having a ROM, a RAM and A/D, D/A conversion functions. In accordancewith a camera-sequence program stored in the ROM, the microcomputer 102implements a series of camera operations, such as automatic exposurecontrol (AE), autofocus (AF) and image sensing. The microcomputer 102controls various circuits and lens operation by communicating withperipheral circuitry within the lens body 101 and with theinterchangeable lens 151. According to the present invention, the ROMconstitutes a storage medium and can be a semiconductor memory, anoptical disk, a magneto-optic device or a magnetic medium, etc.

The mount joining the camera body 101 and the interchangeable lens 151is provided with four connection terminals. A power supply 103 suppliesthe camera circuits and actuators with power-supply voltage and suppliesthe interchangeable lens 151 with power via a line V_(CC).

A line DCL transmits a signal from the microcomputer 102 to amicrocomputer 161 (described later) inside the lens. A line DLCtransmits a signal from the microcomputer 161 inside the lens to themicrocomputer 102 inside the camera body. The camera body 101 controlsthe interchangeable lens 151 via these two lines. The camera body 101and interchangeable lens 151 are connected to ground via a line GND.

The camera body 101 has a display unit 104, such as a liquid crystalpanel, having a display function for displaying photographic conditionsand a monitor function for monitoring a sensed image.

A driver 105 drives and controls an image sensing device 111, describedlater. The driver 105 controls the storage of charge in the imagesensing device 111, charge transfer, CDS (Correlated Double Sampling),AGC (Automatic Gain Control), A/D conversion, gamma correction and AWB(Automatic White Balance), etc.

A memory 106 records and preserves image signal data representing asensed image and can be a semiconductor memory, magnetic disk or opticaldisk, etc.

A terminal 107 for outputting a recorded image to external equipment isconnected to a personal computer or printer.

The image sensing device 111, such as a CCD, is a two-dimensionalphotoelectric sensor for photoelectrically converting the image of theobject formed by an image sensing optical system 152-154.

The camera body has a main switch 120. When this switch is turned on(closed), the microcomputer 102 allows the execution of a prescribedprogram relating to preparations for photography, namely exposuremetering and focus detection, etc.

Switches 121 (SW1) and 122 (SW2) are linked to a camera release buttonand are turned on (closed) by pressing the release button through firstand second stroke lengths, respectively. More specifically, the switch121 is for preparing for image pick-up. When this switch is turned on,preparatory photographic operations, such as exposure metering, focusdetection and focusing, are executed. The switch 122 is a photographyswitch. When this switch is turned on, a photographic image that hasbeen formed on the image sensing device 111 is acquired and recorded inthe image memory 106.

An AF mode switch 123 is used to select the autofocus mode. A displayswitch 124 is used to designate a display for monitoring a photographicimage.

The image of the object formed by the image-sensing optical system isformed again by a focus-detection module 130 using the various opticalelements set forth below. Specifically, the focus-detection module 130includes a first mirror 131 for fully reflecting the photographic lightflux upward in FIG. 1; a semi-transparent second mirror 132 for passingabout 70% of the fully reflected light flux and reflecting the remaining30% of the light flux rightward in FIG. 1; a third mirror 133 for fullyreflecting the light flux downward in FIG. 1; and a fourth mirror 134for fully reflecting the fully reflected light flux rightward in FIG. 1;a field lens 135 placed in a first predetermined focal plane of theimage-sensing optical system, with a primary image IM1 of the object OBJbeing formed in this predetermined focal plane by the image-sensingoptical system; a field mask 136 that decides a focus-detection area;and a pair of secondary image-forming lenses 137 for forming the imagesof the primary image IM1 again.

The entrance pupil of the pair of secondary image-forming lenses 137 andthe exit pupil of a stop 155, described later, are placed in aprojection relationship by the field lens 135. Consequently, twosecondary images IMA and IMB resulting from the light flux that haspassed through different pupil areas (the exit pupil of the stop 155 andthe entrance pupil of the pair of secondary image-forming lenses 137) ofthe image-sensing optical system are formed on the image-sensing device111.

A movable mirror unit 138 is capable of moving the first mirror 131, thefourth mirror 134 and the secondary image-forming lenses 137 in unisonto advance and retract the same into and out of the photographic lightflux.

A quick-return (QR) actuator 139 drives the movable mirror unit 138 toadvance and retract the same.

A focusing screen 141 is placed in a second predetermined focal planethat is in a conjugate relationship with the first predetermined focalplane mentioned above. A secondary primary image IM2 resulting fromlight flux reflected by the first mirror 131 and passed by the secondmirror 132 is formed on the focusing screen 141.

A pentagonal prism 142 and an eyepiece 143 construct an optical finderthat makes it possible for the photographer to view the secondaryprimary image IM2.

The components on the side of the lens will now be described.

The interchangeable lens 151 is capable of being removably mounted onthe camera body 101 and includes a focusing-lens group 152 forperforming focusing by being advanced and retracted along the directionof the optic axis; a zoom-lens group 153 for performing zooming by beingadvanced and retracted along the direction of the optic axis; and arelay-lens group 154 for performing a prescribed image-forming operationtogether with the lens groups 152 and 153. The lens groups 152, 153 and154 together construct the image-sensing optical system.

The stop 155 decides the entrant light flux of the image-sensing opticalsystem, and an actuator 156 drives the stop 155.

Like the microcomputer 102, the microcomputer 161 inside the lens is asingle-chip microcomputer having a ROM, a RAM and A/D, D/A conversionfunctions. In accordance with an instruction sent from the microcomputer102 via the signal line DCL, the microcomputer 161 controls the drivingof a focus actuator and zoom actuator, described later, as well as thedriving of the actuator mentioned above. Various operating states of thelens and parameters specific to the lens are transmitted to themicrocomputer 102 by the signal line DLC.

A focus actuator 162 drives the focusing-lens group 152 to advance andretract the same, and a focus encoder 163 senses position informationindicative of the position of the focusing-lens group 152, namelyobject-distance information. A zoom actuator 164 drives the zoom-lensgroup 153 to advance and retract the same, and a zoom encoder 165 sensesposition information indicative of the position of the zoom-lens group153, namely focal-length information.

<Principles>

First Embodiment

By virtue of the construction described above, the interchangeable lens151 forms the image of the object OBJ on the image sensing device 111 ofthe camera and performs focusing, zooming and control of entrant-lightquantity based upon a control instruction from the camera.

The state of image formation of the object OBJ at the time of focusdetection prior to preparations for photography will now be described.

A light flux from the object OBJ passes through the lens groups 152,153, 154 and stop 155 constructing the image-sensing optical system andis reflected by the first and second mirrors 131, 132, respectively, toform the first primary image IM1 on a first image-forming plane. Thelight flux is then reflected by the third mirror 133, after which thelight flux impinges upon the two secondary image-forming lenses 137.Each of the lenses 137 functions as a pupil. Thus, the lenses 137 formtwo images by pupil-splitting or separating (referred to as simply“splitting”, hereinafter). In other words, two light fluxes are obtainedand these are reflected by the fourth mirror 134, after which thereflected light fluxes are projected onto the light-receiving surface ofthe image-sensing device 111 as the two secondary images IMA and IMB.

FIG. 2 is a diagram showing the state of image formation of thesecondary images IMA, IMB on the image-sensing device 111.

A light-receiving portion 112 of the image sensing device 111 has m×nlight-receiving pixels and a charge-transfer portion (CCDV for verticaltransfer, not shown) for transferring electric charge that hasaccumulated in these pixels. A horizontal transfer portion (CCDH) 113stores electric charge transferred in the direction of arrow TRV by thevertical transfer portion CCDV in the light-receiving portion 112, thentransfers the charge in the direction of arrow TRH and outputs an imagesignal from a signal-output portion 114 to the image-sensor driver 105.

Two areas ARA, ARB on the light-receiving portion 112 are images of thefield mask 136 projected by the secondary image forming lenses 137 ofFIG. 1. The secondary images IMA, IMB of the first primary image IM1 areformed in the areas ARA, ARB, respectively. Let V₀ represent the spacingbetween the two images IMA, IMB when the image-sensing optical system isin focus with respect to the object OBJ.

FIG. 3 is a diagram showing the state of image formation of thesecondary images on the image-sensing device 111 when the image-sensingoptical system is not in focus with respect to the object OBJ. In thiscase the spacing between the two images IMA and IMB is V₁ (≠V₀).

When the switch 121 which prepares the camera body 101 for photographyis closed, stored electric charge in the light-receiving portion 112 isread out, converted from an analog to a digital value and transmitted tothe microcomputer 102. In accordance with a well--known correlationalgorithm, the spacing V₁ between the two above-mentioned images iscalculated and the difference between V₁ and the in-focus spacing V₀,i.e.,

Δv=V ₁ −V ₀

is obtained, thereby making it possible to detect the extent to whichthe object OBJ is out of focus. The amount of such defocus istransmitted to the interchangeable lens 151 and the focusing-lens group152 is driven accordingly to perform an autofocus operation.

FIG. 4 is a diagram showing the camera when the photography switch 122of the camera body 101 is closed upon the completion of the autofocusoperation, thereby establishing the photographic state.

When the photography switch 122 is closed, the movable mirror unit 138is withdrawn away from the optical path of photography (i.e., upward inFIG. 4) by the quick-return actuator 139. When this is done, the mirrorsare removed from between the image-sensing optical system andimage-sensing device 111 so that a primary image IM3 produced by theimage-sensing optical system is formed on the image-sensing device 111.

FIG. 5 is a diagram showing formation of the image of the object on theimage-sensing device 111 at the time of photography. Here the primaryimage IM3 of the object OBJ is projected onto the light-receivingportion 112. Accordingly, the image signal prevailing under theseconditions is accepted and recorded in the image memory 106 of thecamera body 101, whereby the image is sensed.

<Control Procedure>

First Embodiment

FIGS. 6 and 7 are flowcharts illustrating the control flows of themicrocomputers 102, 161 when focus detection, focusing, and photographyare performed by the camera body 101 and interchangeable lens 151according to the first embodiment of the present invention.

The control flow of the microcomputer 102 inside the camera will bedescribed first in accordance with FIG. 6 while making reference to FIG.1.

When the main switch 120 of the camera body 101 is closed (turned on),the microcomputer 102 is activated from the sleep state and controlproceeds from step S101 to step S102, at which the states of theswitches 121-124 inside the camera body 101 are sensed.

The state of the photography-preparation switch 121 (SW1), which isturned on by pressing the release button through its first strokelength, is sensed at step S103. Control returns to step S102 when theswitch 121 is off (open) and proceeds to step S104 when the switch 121is on.

The fact that preparation for shutter release has been executed iscommunicated to the microcomputer 161 inside the interchangeable lens151 at step S104. This is followed by step S105, at which parameters arecommunicated to the microcomputer 161. The communication of parametersinvolves transmitting lens-specific information such as the lensf-number, focal length and focusing sensitivity to the camera.

Next, at step S106, the image-sensing device 111 is activated to acquirean image signal.

Processing of the image signal acquired at step S106 is executed at stepS107. More specifically, processing such as A/D conversion of the imagesignal, white balance adjustment, and gamma correction is executed.

This is followed by step S108, at which object-brightness information iscalculated from the image signal processed at step S107. Further, inaccordance with a predetermined exposure-control program, a controlvalue for narrowing the stop 155 and the exposure time (charge storagetime) of the image sensing device 111 are calculated.

The setting of the AF mode switch 123 is discriminated at step S109 todetermine if the autofocus (AF) mode is in effect. Control proceeds tostep S112 if the mode is not the AF mode and to step S110 if the mode isthe AF mode.

The defocus quantity ΔV of the object is calculated from the spacingbetween the two secondary images IMA, IMB at step S110 in the mannerillustrated in FIG. 3. Next, at step S111, the defocus quantity ΔVcalculated at step S110 is transmitted to the microcomputer 161 insidethe lens.

The state of the photography switch (SW2) 122 is discriminated at stepS112. If the switch 122 is off, control returns to step S102 so that theprocessing of steps S102-S111 is executed again. If the photographyswitch 122 is found to be on at step S112, it is judged that release hasbeen performed and control shifts to step S121.

The transition to the release operation is communicated to themicrocomputer 161 in the lens at step S121. The stop-control value thatwas calculated at step S106 is transmitted to the microcomputer 161 atstep S122.

Next, at step S123, the movable mirror unit 138 is withdrawn from thephotographic optical path of FIG. 1 to the attitude shown in FIG. 4,where the mirror unit 128 is outside the optical path.

Control of charge accumulation and charge transfer in the image sensingdevice is performed at step S124 for the purpose of photography. This isfollowed by step S125, at which processing of the image signal acquiredat step S124 is executed in the same manner as performed at step S107.More specifically, the image signal is applied to A/D conversion, whitebalance adjustment, gamma correction and compression processing, etc.

Next, at step S126, the signal processed at step S125 is recorded andpreserved in the image memory 106. The withdrawn movable mirror unit 138is driven at step S127 so as to be returned to the optical path forphotography. An instruction for restoring the stop 155 is transmitted tothe microcomputer 161 at step S128.

The image recorded at step S126 is displayed on the display unit 104 atstep S129, thereby allowing the photographer to view the image that isthe result of photography.

Control returns to step S102 when the above-described photographicoperation is completed.

FIG. 7 is a flowchart illustrating control of the microcomputer 161inside the lens.

Power is supplied to the interchangeable lens by turning on the mainswitch 120 on the camera side, whereupon control proceeds from step S151to step S152. The microcomputer 161 is in the sleep state waiting forcommunication from the camera body. Control stops at step S152 if thereis no communication from the camera body.

If communication relating to release preparation corresponding to stepS104 in FIG. 6 is received from the microcomputer 102, control proceedsfrom step S152 to step S153.

This is followed by step S153, at which the microcomputer 161 inside thelens senses the states of the focus encoder 163 and zoom encoder 165 andjudges the current status of the lens. Communication of parameterscorresponding to step S105 in FIG. 6 is performed at step S154 basedupon the lens status sensed at step S153.

A signal representing the amount of defocusing corresponding to stepS111 in FIG. 6 is received at step S155.

The amount of focusing-lens drive necessary is calculated at step S156based upon the amount of defocusing received at step S155 and the lensstatus sensed at step S153. Next, at step S157, the focusing lens isdriven to performing focusing based upon the amount of drive calculatedat step S156.

It is determined at step S158 whether a release interrupt correspondingto step S121 of FIG. 6 has occurred. If the decision is “NO”, controlreturns to step S152. If a release interrupt occurs, however, controlproceeds from step S158 to step S171, at which driving of the focusinglens is halted.

A stop-control value is received from the microcomputer 102 at stepS172. Next, at step S173, the stop actuator 156 is driven in accordancewith the stop-control value received at step S172. Photography isperformed on the camera side.

When the photographic operation on the camera side is completed, astop-restoration instruction is received at step S174. The stop isrestored to the open state at step S175 in accordance with thisinstruction.

When the photographic operation on the lens side is completed, controlreturns to step S152.

The operation of the camera and lens according to the foregoingflowcharts will now be summarized.

At the photography preparation stage, the photographic light flux issplit and projected upon the image-sensing device 111 via thefocus-detection optical system in the manner shown in FIG. 1. When themain switch 120 and photography-preparation switch 121 are turned on bythe photographer, the camera calculates the defocus quantity AV of theobject from the spacing between the two secondary images projected uponthe image-sensing device 111, as shown in FIG. 3, and transmits ΔV tothe interchangeable lens 151. In response, the interchangeable lens 151drives the focusing lens in accordance with the defocus quantity ΔV,thereby performing focusing. Next, when the photography switch 122 isturned on, the movable mirror unit 138 is withdrawn from thephotographic light flux, as shown in FIG. 4, so that the in-focus imageof the object is projected upon the image-sensing device 111, as shownin FIG. 5. The camera acquires the image of the object and records theimage in the image memory 106.

<Advantages>

First Embodiment

(AD1) The focus-detection module 130 composed of the four mirrors(131-134) is placed in the optical path between the optical-lens systemand the image-sensing device, and the pair of optical lenses 137 isprovided in the optical path of the focus-detection module 130. Theoptical lens 137 forms two images on the image-sensing device 111 whenthe object is not in focus and forms one image on the image-sensingdevice 111 when the object is in focus. The defocus quantity ΔV can beobtained based upon the spacing V₁ between the two images. As a result,it is unnecessary to separately provide photoelectric conversion meansfor focus detection, and both focus detection and focusing can beperformed using the light flux that has passed through the photographiclens. This makes it possible to realize an inexpensive, small-sizecamera exhibiting highly accurate automatic focusing.

(AD2) The focus-detection module 130 is disposed in back of the finallens group (the lens group 154 in the example of FIG. 1) of theimage-sensing optical system. As a result, the module is suited to adigital still camera of the single-lens reflex type having a long backfocus.

(AD3) Part of the photographic-light flux is split by a beam splitter(the mirror 132) before being introduced to the optical finder system(the pentagonal prism 142 and eyepiece 143). This makes it possible toobtain a high-quality optical finder and to visually confirm the stateof focus of an object image in a highly accurate manner. The opticalpath of the optical finder system and part of the optical path of thefocus-detection module 130 can be made to coincide, thereby making itpossible to reduce the size of the overall camera.

<Modifications>

First Modification

(M1) If there is no limitation upon the size of the camera overall, theoptical path of the optical finder system and the optical path of thefocus-detection module 130 may be separated completely. In such case ahalf-mirror (132′, not shown in figures) such as the mirror 132 isprovided between the lens 154 and the mirror 121, and the mirror 132 ismade a fully reflective mirror. The optical finder is disposed above themirror 132′.

(M2) The lenses 137 for splitting the optic axis into two portionsshould ideally be provided between the mirror 133 and the mirror 134.Theoretically, however, it is possible to provide the lenses 137 betweenthe lens 135 and mirror 133 or between the mirror 132 and lens 135.

<Second Embodiment>

According to the first embodiment set forth above, the pair of secondaryimage-forming lenses 137 are arranged parallel to the light-incidentdirection onto the photographic screen 111 (that is, in a right-to-leftdirection with respect to the FIG. 1 orientation) so that the twosecondary images (IMA and IMB) are disposed one above the other on thephotographic screen 111. In the second embodiment described below, apair of secondary image-forming lenses are adapted (in a directionvertical to the surface of FIG. 1 drawing) to be arranged so that twosecondary images are juxtaposed side by side on the photographic screenand are vertically offset from the optic axis. Specifically, theconstruction of the second embodiment is substantially identical to thatof the first embodiment except for the arrangement of secondary forminglenses.

FIG. 8 is a perspective view showing a development of part of thefocus-detection optical system according to the second embodiment, andFIG. 9 is a plan view showing the disposition of the secondary images onthe image-sensing device 111. The construction and operation of thisembodiment will now be described.

Elements other than those shown in FIG. 8 are identical with those ofthe first embodiment illustrated in FIG. 1.

FIG. 8 schematically illustrates an optical path from the field mask 136to the image-sensing device 111. In FIG. 8, the third mirror 133 and thefourth mirror 134 are omitted from the focus-detection module 130 inFIG. 1 for the sake of simplified illustration purpose.

According to the second embodiment as shown in FIG. 8, the pair of twosecondary image-forming lenses 237 are disposed horizontally, i.e., sideby side with respect to the photographic screen, between the field lens135 (having the field mask 136) and the image sensing device 111. Thecenters connecting the two secondary image-forming lenses 237 are offsetby a distance OFS to a position below the optic axis C. Accordingly, theprojected images of the field mask 136 formed by the secondaryimage-forming lenses 237 become downwardly offset areas ARC, ARD on thelight-receiving portion 112 of the image-sensing device 111.

FIG. 9 illustrates the disposition of images on the image-sensing device111 in the arrangement of FIG. 8. The images ARC, ARD of the field mask136 are projected as areas on the light-receiving portion 112, andsecondary images IMC, IMD of the object OBJ are formed in the areas ARC,ARD, respectively. Let H₀ represent the spacing between the two imageswhen the object is in focus, and let H₁ represent the spacing betweenthe two images when the object is not in focus. If H₁ is measured and H₀and H₁ can be compared, then a defocus quantity ΔH (=H₁−H₀) of theobject OBJ can be detected.

In FIG. 9, the two secondary image-projection areas ARC, ARD aredisposed at the lower part the light-receiving portion 112, namely onthe side near the exit in the transfer direction of thevertical-transfer CCD in the light-receiving portion. As a result, onlythe image signal on the lower half of the light-receiving portion 112need be read for the purpose of detecting focus. In other words, if theimage signal on the lower half of the light-receiving portion 112 isused in image processing for focus detection, then the image signal ofthe upper half of the light-receiving portion 112 maybe discardedwithout being read. In the first focus-detection cycle, therefore, thetime needed to read out the image signal is shortened.

The flowcharts for controlling the camera and interchangeable lens inthis embodiment are the same as the control flowcharts of the firstembodiment shown in FIGS. 6 and 7 and need not be described again.

The second embodiment has the following advantage in addition to theadvantages (AD1)-(AD3) of the first embodiment:

Since the image-signal readout time for detecting focus is shortened, itis possible to speed up the focus detection operation or autofocusoperation.

<Third Embodiment>

In the first and second embodiments, focus detection is carried outbased upon one pair of secondary images. In the third embodimentdescribed below, the optical system is so adapted that focus-detectionis carried out by forming two pairs of secondary images.

FIG. 10 is a perspective view showing a development of part of thefocus-detection optical system according to the third embodiment, andFIG. 11 is a plan view showing the disposition of the secondary imageson the image-sensing device 111. The construction and operation of thisembodiment will now be described.

In FIG. 10, two pairs of secondary image-forming lenses 337 are disposedbetween the field lens 135 (having the field mask 136) and theimage-sensing device 111. The projected images of the field mask 136formed by the secondary image forming lenses 337 become four areas ARA,ARB, ARC and ARD on the light-receiving portion 112 of the image-sensingdevice 111.

Elements other than those shown in FIG. 10 are identical with those ofthe first embodiment illustrated in FIG. 1.

FIG. 11 illustrates the disposition of images on the image-sensingdevice 111 in the arrangement of FIG. 10. The images ARA, ARB, ARC, ARDof the field mask 136 are projected on the light-receiving portion 112,and secondary images IMA, IMB, IMC, IMD of the object OBJ are formed inthe areas ARA, ARB, ARC, ARD, respectively. Let V₀ represent the spacingbetween the two images IMA, IMB when the object is in focus, and let Horepresent the spacing between the two images IMC, IMD when the object isin focus. If the spacings between the images when the object is not infocus are measured and compared with the spacings V₀ and H₀, then adefocus quantity of the object OBJ can be detected.

Except for the fact that two sets of operations for detecting the amountof defocusing of the image of the object are provided in the thirdembodiment, the flowcharts for controlling the camera andinterchangeable lens in this embodiment are the same as the controlflowcharts of the first embodiment shown in FIGS. 6 and 7 and need notbe described again.

The third embodiment has the following advantage in addition to theadvantages (AD1)-(AD3) of the first embodiment:

Since focus detection is carried out based upon images of the object OBJthat are offset vertically and horizontally, focus detection can beperformed with greater accuracy.

<Fourth Embodiment>

In the first through third embodiments described above, the secondaryimage-forming optical system for focus detection uses mirrors fordeflecting the light flux. In the fourth embodiment described below, useis made of a reducing lens instead of mirrors.

FIGS. 12-17 are diagrams relating to the fourth embodiment.

FIG. 12 is a diagram showing the construction of an image-sensingapparatus according to the present invention. This shows the apparatuswhen detection of focus is carried out. According to this embodiment,the focus-detection module 130 of the first embodiment shown in FIG. 1is replaced by a focus-detection module 430. Though the optical findercomposed of such elements as the pentagonal prism is eliminated, otherelements are the same as those shown in FIG. 1. The construction andoperation of this embodiment will now be described.

As shown in FIG. 12, the focus-detection module 430 includes a reducinglens 431, a field mask 436, a field lens 435 and two secondaryimage-forming lenses 437. The stop 155 of the interchangeable lens 151and the entrance pupil of the pair of secondary image-forming lenses 137are in a projection relationship owing to the field lens 135. Aquick-return (QR) actuator 439 is provided for advancing and retractingthe focus-detection module 430 into and out of the projected light flux.

The image of the object OBJ is formed as a primary image IM4 on theprimary image-forming surface in the field lens 435 via theimage-sensing optical system, which is constructed by the lens groups152-154 and stop 155, and the above-mentioned reducing lens 431. Itshould be noted that the primary image IM4 has a size different fromthat of the first primary image IM1 or IM2 of the first embodiment owingto the intervention of the reducing lens 431.

The primary image IM4 is split by the two secondary image forming lenses437 disposed one above the other, whereby the image is formed again.These secondary images are projected upon the image sensing device 111as IMA and IMB.

FIG. 13 is a diagram showing formation of the secondary images on theimage sensing device 111. In a manner similar to that of the firstembodiment, this embodiment detects the amount of defocusing of theobject OBJ based upon a change in the difference between the two imageswith respect to the reference spacing value V₀ between the images.

FIG. 14 illustrates the state of the display presented on a display unit404 when focus detection is performed. One of the two secondary images,e.g., IMB, projected upon the image-sensing device 111 in FIG. 13 issubjected to enlargement processing and displayed on the display unit404 as IMBL, thereby making it possible for the photographer to checkthe composition of the photographic area as well as the state offocusing.

FIG. 15 is a diagram showing the camera when the photography switch 122of the camera body 101 is closed upon the completion of the autofocusoperation, thereby establishing the photographic state.

When the photography switch 122 is closed, the entire focus-detectionmodule 430 is withdrawn away from the optical path of photography (i.e.,upward in FIG. 15) by the quick-return actuator 439.

FIG. 16 is a diagram showing formation of the image of the object on theimage-sensing device 111 at the time of photography. Here the primaryimage IM3 of the object OBJ is projected onto the light-receivingportion 112 in a manner similar to that of the first embodiment.Accordingly, the image signal prevailing under these conditions isaccepted and recorded in the image memory 106 of the camera body 401,whereby the image is sensed.

FIG. 17 is a flowchart illustrating the control flow of a microcomputer402 inside the camera body. This flowchart differs from that of FIG. 6only in the addition of an operation for displaying a finder image atthe time of focus detection.

When the main switch 120 of the camera body 401 is turned on, themicrocomputer 402 is activated from the sleep state and control proceedsfrom step S401 to steps S402, S403 and S404.

The fact that preparation for shutter release has been executed iscommunicated to the microcomputer 161 inside the interchangeable lens151 at step S404. This is followed by step S405, at which parameters arecommunicated to the microcomputer 161.

Next, at step S406, the image sensing device 111 is activated to acquirean image signal.

Processing of the image signal acquired at step S406 is executed at stepS4107. More specifically, processing such as A/D conversion of the imagesignal, white balance adjustment, and gamma correction is executed.

This is followed by step S408, at which the image to be displayed on thedisplay unit 404, namely the image in the area ARB of FIG. 13, isenlarged and then rotated by 180° about its center. In comparison withthe image that prevails at the time of imaging, therefore, the image isturned upside down when focus detection is performed.

The image for viewing purposes obtained at step S408 is displayed on thedisplay unit 404 at step S409.

This is followed by step S410, at which object brightness information iscalculated from the image signal processed at step S407. Further, inaccordance with a predetermined exposure-control program, a controlvalue for narrowing the stop 155 and the exposure time (charge storagetime) of the image sensing device 111 are calculated.

The setting of the AF mode switch 123 is discriminated at step S411 todetermine if the autofocus (AF) mode is in effect. Control proceeds tostep S414 if the mode is not the AF mode and to step S412 if the mode isthe AF mode.

The amount of defocus of the object is calculated from the spacingbetween the two secondary images at step S412 in the manner illustratedin FIG. 13. Next, at step S413, the amount of defocus calculated at stepS412 is transmitted to the microcomputer 161 inside the lens.

The state of the photography switch 122 is discriminated at step S414.If the switch 122 is off, control returns to step S402. If thephotography switch 122 is found to be ON, it is judged that release hasbeen performed and control shifts to step S421.

The release sequence of steps S421-S429 is the same as the processing ofsteps S121-S129 in FIG. 6 and need not be described again. Further, theflow for controlling the interchangeable lens 151 is the same as that ofthe first embodiment shown in FIG. 7 and need not be described again.

The operation of the camera and lens according to the foregoing flowwill now be summarized.

At the photography preparation stage, the photographic light flux issplit and projected upon the image-sensing device 111 via thefocus-detection module 430 in the manner shown in FIG. 12. When the mainswitch 120 and photography preparation switch 121 are turned on by thephotographer, the camera enlarges one of the two secondary images, whichare projected upon the image-sensing device 111 in the manner shown inFIG. 13, and displays the enlarged image on the display unit 404, asillustrated in FIG. 14. Next, the camera calculates the amount of objectdefocus from the spacing between the two secondary images and transmitsthis to the interchangeable lens 151. In response, the interchangeablelens 151 drives the focusing lens in accordance with the defocusquantity, thereby performing focusing. Next, when the photography switch122 is turned on, the focus-detection module 430 is withdrawn from thephotographic light flux, as shown in FIG. 15, so that the in-focus imageof the object is projected upon the image-sensing device 111, as shownin FIG. 16. The camera acquires the image of the object and records theimage in the image memory 106.

The fourth embodiment has the following advantages in addition to theadvantages (AD1), (AD2) of the first embodiment:

(AD6) A mirror for deflecting the optical path is not required in thefocus-detection module 430, thereby making it possible to reduce thesize of the module and simplify the same.

(AD7) Since the image for purposes of focus detection is displayed onthe monitor screen of the display unit, an optical finder isunnecessary. This makes it possible to reduce the size and lower thecost of the apparatus.

<Fifth Embodiment>

In the fourth embodiment described above, the reducing lens is used inthe optical system for focus detection. In a fifth embodiment describedbelow, however, a relay lens is inserted into the optical system forfocus detection and the reducing lens is not employed.

FIGS. 18 and 19 are diagrams relating to the fifth embodiment.

FIG. 18 is a diagram showing the construction of an image sensingapparatus according to the present invention. This shows the apparatuswhen detection of focus is carried out. According to this embodiment,the focus-detection module 430 of FIG. 12 is replaced by afocus-detection module 530, and a relay lens module 540 is additionallyprovided. A lens 531 is provided at the rearmost portion of theimage-forming optical system inside an interchangeable lens 551. Othercomponents are the same as shown in FIG. 12.

As shown in FIG. 18, the focus-detection module 530 includes a fieldmask 536, a field lens 535 and a pair of secondary image-forming lenses537. The stop 155 of the interchangeable lens 551 and the entrance pupilof the pair of secondary image-forming lenses 537 are in a projectionrelationship owing to the field lens 535.

The relay lens module 540 is provided internally with a concave relaylens 541. A quick-return actuator (QR) 539 is provided for moving thefocus-detection module 530 and relay lens module 540 into thephotographic light flux alternatively.

The image of the object OBJ is formed as a primary image IM5 on theprimary image-forming surface in the field lens 535 via theimage-sensing optical system, which is constructed by the lens groups152-154, stop 155 and lens 531. The arrangement is such that the primaryimage IM5 has a size substantially the same as that of the image IM4 ofthe fourth embodiment.

The primary image IM5 is split by the two secondary image forming lenses437, whereby the image is formed again. These secondary images areprojected upon the image-sensing device 111 as IMA and IMB. Theprojected images are the same as those shown in FIG. 13. In addition,the viewing image displayed on a display unit 504 is similar to thatshown in FIG. 14.

FIG. 19 is a diagram showing the camera when the photography switch 122of the camera body 501 is closed upon the completion of the autofocusoperation, thereby establishing the photographic state.

When the photography switch 122 is closed, the entire focus-detectionmodule 530 is withdrawn away from the optical path of photography (i.e.,upward in FIG. 19) by the quick-return actuator 539. The relay lensmodule 540 is inserted into the photographic optical path in place ofthe focus-detection module 530. When this is done, the primary image IM3formed by the image-sensing optical system in the interchangeable lens551 and the relay lens 541 in the camera body 501 is formed on theimage-sensing device 111. The state of the formed image is the same asthat of the primary image shown in FIG. 16. Accordingly, the imagesignal prevailing under these conditions is accepted and recorded in theimage memory 106 of the camera body 501, whereby the image is sensed.

The control flow of this embodiment is the same as that of the fourthembodiment and need not be described again.

The fifth embodiment has the following advantages in addition to theadvantages (AD1), (AD2) of the first embodiment and the advantages(AD6), (AD7) of the fourth embodiment:

(AD8) Since use is made of the relay lens 541 advanced and retracted atthe time of photography, greater freedom is provided in terms of opticaldesign and the optical system can be reduced in size and improved inperformance.

(AD9) The optical structure of the focus-detection module 530 issimplified and optical aberration of this module can be reduced toimprove the accuracy of focus detection.

It should be noted that the focus-detection optical system of the secondor third embodiment may be applied to the fourth or fifth embodiment.Further, a half-mirror may be placed in front of the focus-detectionmodule of the fourth or fifth embodiment to extract part of thephotographic light flux and introduce this flux to an optical finder.Furthermore, the invention may be applied not only to an image sensingapparatus of interchangeable lens type but also to an image-sensingapparatus having a fixed lens.

<Sixth Embodiment>

FIGS. 20 through 24 are diagrams relating to the sixth embodiment.

FIG. 20 is a block diagram showing the construction of an image sensingapparatus according to a sixth embodiment.

Numeral 601 denotes a camera body having various functional componentsfor forming the image of an object OBJ, detecting focus and sensing theimage.

The camera body includes the focusing-lens group 152 for performingfocusing by being advanced and retracted along the direction of theoptic axis; the zoom-lens group 153 for performing zooming by beingadvanced and retracted along the direction of the optic axis; and therelay-lens group 154 for performing a prescribed image-forming operationtogether with the lens groups 152 and 153. The stop 155 decides theentrant light flux of the image-sensing optical system.

An infrared blocking filter 606 blocks infrared light from the objectOBJ and passes only visible light. The lens groups 152, 153, 154, thestop 155, and the infrared blocking filter 606 together construct theimage-sensing optical system. A first IM1 of the object OBJ is formed ona main image sensing device 111.

As in the first and other embodiments, the main image-sensing device 111is a two-dimensional photoelectric sensor, such as a CCD, forphotoelectrically converting the first image IM1.

The camera body further includes a rangefinding module 621 having alight-receiving lens 622 for forming the image of the object OBJ whoserange is to be measured, an infrared blocking filter 623 for blockinginfrared light and passing only visible light of the light flux that haspassed through the light-receiving lens 622, and a subordinateimage-sensing device 624. The rangefinding optical system, whichincludes the light-receiving lens 622 and the infrared blocking filter623, has an image forming power different from that of theabove-mentioned image-sensing optical system and forms a second imageIM2 of the object OBJ on the subordinate image sensing device 624,described later.

The subordinate image sensing device 624, such as a CCD, is atwo-dimensional photoelectric sensor for photoelectrically convertingthe second image IM2. The module 621 including these elements is sodisposed that its optic axis is spaced away from the optic axis of theimage-sensing optical system by a distance equivalent to a baselengthBL.

A microcomputer 631 is a single-chip microcomputer having a ROM, a RAMand A/D, D/A conversion functions. In accordance with a camera sequenceprogram stored in the ROM (not shown), the microcomputer 631 implementsa series of camera operations, such as automatic exposure control (AE),autofocus (AF) and image sensing. To this end, the microcomputer 631controls the operation of peripheral circuits and actuators inside thecamera body 601. According to the present invention, the ROM constitutesa storage medium and can be a semiconductor memory, an optical disk, amagneto-optic disk or a magnetic medium, etc.

The power supply 103 supplies the camera circuits and actuators withpower.

The driver 105 drives and controls the main image sensing device 111.The driver 105 controls the storage of charge in the image-sensingdevice 111, charge-transfer, CDS (Correlated Double Sampling), AGC(Automatic Gain Control), A/D conversion, gamma correction and AWB(Automatic White Balance), etc.

A driver 634 drives and controls the subordinate image-sensing device624 and, like the driver 105 of the main image-sensing device, controlsthe storage of charge in the image-sensing device 111, the chargetransfer, the CDS, the AGC, the A/D conversion, the gamma correction andthe AWB, etc.

The memory 106 records and preserves image signal data representing animage sensed by the main-image-sensing device 111 and can be asemiconductor memory, an optical disk, a magneto-optical disk or amagnetic medium, etc.

The terminal 107 for outputting a recorded image to external equipmentis connected to a personal computer or printer.

The camera body has a display unit 104, such as a liquid crystal panel,having a display function for displaying photographic conditions and amonitor function for monitoring a photographic image.

As in the first embodiment, the camera body has the main switch 120.When this switch is turned on, the microcomputer 631 allows theexecution of a prescribed program relating to preparations forphotography, namely exposure metering and focus detection, etc.

The switches 121 and 122 are linked to the camera release button and areturned on by pressing the release button through first and second strokelengths, respectively. More specifically, the switch 121 is forpreparing for picture taking. When this switch is turned on, preparatoryphotographic operations, such as exposure metering, focus detection andfocusing, are executed. The switch 122 is a photography switch. Whenthis switch is turned on, a photographic image that has been formed onthe image sensing device 111 is acquired and recorded in the imagememory 106.

The AF mode switch 123 is used to select the autofocus mode. The displayswitch 124 is used to designate a display for monitoring a photographicimage.

The focus actuator 162 drives the focusing-lens group 152 to advance andretract the same, and the focus encoder 163 senses position informationindicative of the position of the focusing-lens group 152, namelyobject-distance information. The zoom actuator 164 drives the zoom-lensgroup 153 to advance and retract the same, and the zoom encoder 165senses position information indicative of the position of the zoom-lensgroup 153, namely focal-length information.

The stop actuator 156 controls the stopping down of the stop 155 andrestores the stop 155 to the open state.

By virtue of the construction described above, the camera body 601acquires the first image IM1 and second image IM2 of the object OBJ andperforms rangefinding, focusing, and image sensing through methodsdescribed later.

<Principles>

Sixth Embodiment

The state of image formation of the object OBJ at the time of focusdetection prior to preparations for photography will now be described.

A light flux from the object OBJ passes through the image-sensingoptical system comprising the lens groups 152, 153, 154 and is formed onthe main image-sensing device 111 as the first image IM1. Further, thesecond image IM2 is formed on the subordinate image-sensing device 624inside the rangefinding module 621.

FIGS. 21A, 21B are diagrams illustrating the two image-sensing devices111, 624 and the dispositions of two images formed on theseimage-sensing devices.

The light-receiving portion 112 of the image sensing device 111comprises m₁×n₁ light-receiving pixels and a charge-transfer portion(vertical transfer CCD) for transferring electric charge that hasaccumulated in these pixels. The horizontal transfer CCD 113 storeselectric charge transferred in the direction of arrow TRV by thevertical transfer CCD in the light-receiving portion 112, then transfersthe charge in the direction of arrow TRH and outputs an image signalfrom the signal-output portion 114 to the image-sensor driver 105.

In FIG. 21B, IM1 _(T) represents the image of the object OBJ when theimage-sensing optical system has been set to the maximum telescopicmode, and IM1 _(W) represents the image of the object OBJ when theimage-sensing optical system has been set to the maximum wide-anglemode. Thus, the size of the first image IM1 of the object variesdepending upon the state of the image-sensing optical system.

A light-receiving portion 625 of the subordinate image-sensing device624 comprises m₂×n₂ light-receiving pixels and a charge transfer portion(vertical transfer CCD) for transferring electric charge that hasaccumulated in these pixels. A horizontal transfer CCD 626 storeselectric charge transferred in the direction of arrow TRV by thevertical transfer CCD in the light-receiving portion 625, then transfersthe charge in the direction of arrow TRH and outputs an image signalfrom the signal output portion 627 to the image-sensor driver 634.

In FIG. 21A, IM2 _(INF) represents the image obtained when the objectOBJ is at infinity, and IM2 _(DEF) represents the image obtained whenthe object OBJ is at a finite distance. Thus, the position of the secondimage IM2 of the object varies depending upon the distance of the objectOBJ.

FIGS. 22A, 22B are diagrams useful in describing the principle of imagemagnification correction for detecting object distance from the firstand second images IM1 and IM2, respectively, of the object.

According to the principle of rangefinding by triangulation, a disparityin regard to the object is detected from the relative positions of twoimages formed by two image-forming systems spaced apart by apredetermined baselength, and the object distance is found from thisdisparity. In this case, it is required that the sizes of the two imagesbe equalized. However, as described above in connection with FIGS. 21A,21B, the first image IM1 varies in size depending upon the zoom settingof the image-sensing optical system. Even if the two images have thesame optical size, the number of pixels (or pixel size) of thelight-receiving portion 112 of image-sensing device 111 and the numberof pixels (or pixel size) of the light-receiving portion 625 ofimage-sensing device 624 differ. Consequently, if the image signal isprocessed digitally, it is necessary to subject the image to a magnitudecorrection based upon the difference in the numbers of pixels.

In this embodiment, the image forming characteristics of theimage-sensing optical system are recognized from the results ofdetection from the focus encoder 163 and zoom encoder 165 inside thecamera body 601, and the size of the first image IM1 is made equal tothe size of the second image IM2 based upon the results of recognition.

FIGS. 22A, 22B are diagrams illustrating the respective images afterapplication of the above-described size correction. FIGS. 21A, 21Billustrate the sizes of the optical images on the image sensing devices624, 111, while FIGS. 22A, 22B conceptually illustrate the image signalsin image computation memories (not shown in FIG. 20) within themicrocomputer 631. In FIG. 22A, IM2 _(DEF) represents the image signalread out of the subordinate image sensing device 624 and stored in asecond computation memory RAM2, and IM1 ₀ represents the image signalread out of the main image sensing device 111 and stored in a firstcomputation memory RAM1. The signal IM1 ₀ is an image signal that hasundergone the size correction described above. As the result of the sizecorrection, the image IM2 _(DEF) regarding the second image IM2 of theobject and the image IM1 ₀ regarding the first image IM1 of the objectare the same in size but and differ only in terms of their relativepositions, as illustrated in FIG. 23.

FIG. 23 is a schematic view showing spacing V_(DEF) of image signalsstored in the two computation memories RAM1, RAM2 mentioned above.

In accordance with a well-known correlation algorithm, the distanceV_(DEF) of the image IM2 _(DEF) relative from the image IM1 ₀ isobtained and distance DST to the object OBJ can be calculated from thefollowing equation using a reference spacing V₀, the focal length f ofthe light-receiving lens 622 and baselength BL of the rangefindingmodule 621: $\begin{matrix}{{DST} = \frac{f \cdot {BL}}{\Delta \quad V}} & \left( {{EQ}.\quad 1} \right)\end{matrix}$

where the following holds:

ΔV=V _(DEF) −V ₀  (EQ.2)

Ideally, the reference spacing V₀ should be zero when the object is atinfinity. In general, however, the optical systems and image-sensingelements develop positional offsets in the camera-manufacturing process.According to this embodiment, therefore, information representing thereference spacing V₀ conforming to the positions of the focusing-lensgroup 152 and zoom-lens group 153 is stored in the ROM (not shown) ofthe microcomputer 631.

FIG. 24 is a flowchart showing the control flow of the microcomputer 631when focus detection, focusing and photography are performed in thecamera body 601 according to the sixth embodiment.

<Control Procedure>

Sixth Embodiment

The control flow of FIG. 24 will be described while making reference toFIGS. 20 through 23.

When the main switch 120 of the camera body 101 is turned on, themicrocomputer 631 is activated from the sleep state and control proceedsfrom step S501 to step S502, at which the states of the switches 121-124inside the camera body 601 are sensed.

The state of the photography preparation switch 121 (SW1), which isturned on by pressing the release button through its first strokelength, is sensed at step S503. Control returns to step S502 when theswitch 121 is off and proceeds to step S504 when the switch 121 is on.

Next, at step S504, the main image-sensing device 111 is activated toacquire an image signal.

Processing of the image signal acquired at step S504 is executed at stepS505. More specifically, processing such as A/D conversion of the imagesignal, white balance adjustment and gamma correction, is executed.

This is followed by step S506, at which object-brightness information iscalculated from the image signal processed at step S505. Further, inaccordance with a predetermined exposure-control program, a controlvalue for stopping down the stop 155 and the exposure time (chargestorage time) of the image sensing device 111 are calculated.

The image signal produced by the image sensing device 111 at steps S504and S505, namely the image signal 1M1 _(W) or 1M1 _(T) in FIG. 21B, isdisplayed on the display unit 104 at step S507.

Next, the setting of the AF mode switch 123 is discriminated at stepS508 to determine if the autofocus (AF) mode is in effect. Control jumpsto step S520 if the mode is not the AF mode and proceeds to step S511 ifthe mode is the AF mode. The autofocus operation, described below, isthen executed.

The microcomputer 631 senses the state of the focus encoder 163 at stepS511 and senses the state of the zoom encoder 165 at step S512 to judgethe current optical status of the lens.

A coefficient for making the size of the first image IM1 of the objectequal to that the second image of the object, namely animage-magnification correction coefficient, is read out of the ROM (notshown) of microcomputer 631 at step S513 in the manner described abovein connection with FIGS. 22A, 22B. Coefficients are stored in the ROM asmatrix data corresponding to the states of the focus encoder 163 andzoom encoder 165.

Next, a position-offset correction quantity V₀ is read out of ROM atstep S514 in the same manner as the image-magnification correctioncoefficient.

The subordinate image-sensing device 624 is activated at step S515 toobtain an image signal.

Processing of the image signal acquired at step S515 is executed at stepS516. More specifically, processing such as A/D conversion of the imagesignal, white balance adjustment and gamma correction, is executed.

This is followed by step S517, at which image size is corrected bymultiplying the image signal of the first image IM1 acquired at stepS505 by the image-magnification correction coefficient read out at stepS513.

Next, at step S518, the distance to the object is calculated inaccordance with Equations (EQ.1), (EQ.2) using the first image IM1 whosesize has been corrected at step S517, the second image IM2 obtained atstep S516 and the position-offset correction quantity V₀ obtained atstep S514.

The focusing lens group 152 is driven at step S519 based upon the resultof the above-described calculation to bring the first image IM1, whichis for image sensing purposes, into focus.

The state of the photography switch 122 (SW2) is discriminated at stepS520. If the switch 122 is off, control returns to step S502 so that theprocessing of steps S502-S519 is executed again. If the photographyswitch 122 is found to be on at step S520, it is judged that release hasbeen performed and control shifts to step S521.

The stop actuator 166 is driven at step S521 in accordance with thestop-control value calculated at step S506.

Charge accumulation and charge transfer of the main image-sensing device111 for photography are controlled at step S522. This is followed bystep S523, at which processing of the image signal acquired at step S522is executed in the same manner as performed at step S505. Morespecifically, the image signal is applied to A/D conversion, whitebalance adjustment, gamma correction, and compression processing, etc.

Next, at step S524, the signal processed at step S523 is recorded andpreserved in the image memory 106. The image recorded at step S524 isdisplayed on the display unit 104 at step S525, thereby allowing thephotographer to check the image that is the result of photography.

The stop actuator 166 is restored to open the stop 155 at step S526.

Control returns to step S502 when the above-described photographicoperation is completed.

The operation of the camera according to the foregoing flowchart willnow be summarized.

At the photography-preparation stage, the first image IM1 of the objectis formed on the image-sensing device 111 via the image sensing opticalsystem and the second image IM2 of the object is formed on thesubordinate image sensing device 624 via the light-receiving lens 622,as illustrated in FIG. 20 and FIGS. 21A, 21B.

When the main switch 120 and photography preparation switch 121 areturned on by the photographer, the camera obtains the twoabove-mentioned images, performs the image-magnification correction, asshown in FIGS. 22A, 22B, and calculates the distance to the object OBJby calculating the spacing between the two images in the manner shown inFIG. 23. The focusing-lens group 152 is driven based upon the calculatedvalue, whereby focusing is achieved. Continuous focusing is performed byexecuting this operation repeatedly. Meanwhile, the first image IM1 ofthe object is displayed on the display unit 104 to inform thephotographer of the composition of the picture taken and of the state offocusing.

When the photography switch 122 is turned on, the image of the objectprojected upon the image-sensing device 111 is recorded in the imagememory 106 and image of the picture taken is displayed on the displayunit 104.

<Advantages>

Sixth Embodiment

The sixth embodiment provides the following advantages:

(AD10) The rangefinding module can be simplified to make possible anautofocus camera that is compact and low in price.

(AD11) The image-sensing optical system serves also as the rangefindingoptical system. As a result, when telescopic photography requiring moreaccurate rangefinding is performed, the image of the object forrangefinding purposes is also projected in enlarged size. This makes itpossible to achieve a rangefinding accuracy that conforms to the stateof the image sensing optical system.

(AD12) Parameter correction, e.g., correction of image magnification, atthe time of rangefinding computation is carried out using a rangefindingparameter that conforms to the state of the image sensing opticalsystem. Even if the state of the image sensing optical system changes,therefore, accurate detection of object distance is possible at alltimes.

(AD13) The autofocus operation is executed repeatedly at the photographypreparation stage. This makes it possible to shorten release time lagfrom issuance of a photography-start instruction to implementation ofimage sensing.

(AD14) Since the automatically focused image of the object is displayedon the display unit 104, such as a liquid crystal monitor, the state offocus of the image of the object can be verified visually and accuratelyin real-time.

<Seventh Embodiment>

The sixth embodiment concerns a passive-triangulation-type rangefindingdevice composed of a single image-sensing system and a singlerangefinding module. A seventh embodiment described below provides anactive-triangulation-type rangefinding device (i.e., a device in whichinfrared light is projected upon an object and rangefinding is performedbased upon the reflected light) comprising a single image-sensing systemand a single projection system.

<Seventh Embodiment>

FIGS. 25 through 31 are diagrams for describing the construction andoperation of the seventh embodiment. FIG. 25 illustrates the dispositionof the image-sensing apparatus when rangefinding is performed accordingto the seventh embodiment. Components in FIGS. 25 through 31 thatperform actions identical with those of the sixth embodiment aredesignated by like reference characters and need not be described againin detail.

Numeral 701 denotes a camera body having various functional componentsfor forming the image of an object OBJ, detecting focus and sensing theimage. The image sensing optical system is composed of the elements152-155 of the sixth embodiment.

An infrared blocking filter 706 blocks infrared light from the objectOBJ and passes only visible light. Since the filter 706 is used forordinary image sensing, it is withdrawn from the light flux of thesensed image at the time of rangefinding (shown in FIG. 25).

An infrared passing filter 707 blocks visible light and passes onlyinfrared light from the object OBJ. Since the filter 707 is used forrangefinding, the filter is inserted into the light flux of the sensedimage only at the time of rangefinding. The lens groups 152, 153, 154,stop 155 and filters 706, 707 together construct the image-sensingoptical system.

Numeral 711 denotes an image-sensing device, such as a CCD. This is atwo-dimensional photoelectric sensor for photoelectrically convertingthe object image, which is for image-sensing purposes, or the image ofan infrared spot which is for rangefinding, described later. Theimage-sensing device 711 is sensitive to light from the visible toinfrared wavelengths.

A projection module 721 includes a light-emitting element 724 that emitsinfrared light from a light-emitting portion 723, and a projecting lens722 for projecting the emitted infrared light onto the object OBJ. Theprojection module 721 having these elements is spaced away from theoptic axis of the image-sensing optical system by the baselength BL. Asa result, a rangefinding pattern that corresponds to the projected imageof the light-emitting portion 723, namely an infrared spot SPT, isformed on the object OBJ. The infrared spot SPT is formed, via theimage-sensing optical system, as an infrared spot image SPT₁ on the mainimage-sensing device 711 at a position spaced a predetermined distanceaway from the center thereof. Since the infrared-passing filter 707 hasbeen inserted into the light flux of the sensed image, the light flux ofthe object OBJ per se does not pass through the filter; only the lightflux from the infrared spot SPT arrives at the main image-sensing device711.

A driver 734 drives the light-emitting element 724 so that the latteremits rangefinding infrared light at the time of a rangefindingoperation in accordance with an instruction from a microcomputer 731.

The microcomputer 731 is a single-chip microcomputer having a ROM, a RAMand A/D, D/A conversion functions. In accordance with a camera sequenceprogram stored in the ROM serving as a storage medium, the microcomputer731 implements a series of camera operations, such as automatic exposurecontrol (AE), autofocus (AF) and image sensing in a manner similar tothat of the sixth embodiment. To this end, the microcomputer 731controls the operation of peripheral circuits and actuators inside thecamera body 701.

The power supply 103, the driver 105, the memory 106, the terminal 107,the display unit 104 and the switches 120-124, 162-166 are similar tothose of the sixth embodiment.

An optical finder 761 is composed of a lens group 762, a zoom lens 762,an erecting prism 764 such as a Porro lens, a field mask 765 and aneyepiece 766. A zoom linkage member 767 mechanically connects the zoomlens 153 with the zoom lens 763. The magnification of the optical finder761 is automatically adjusted by the zoom linkage member 767 inoperative association with the zooming operation of the image-sensingoptical system. An exposure-metering element 768 is disposed in thevicinity of the optical finder 761. The exposure metering element 768splits the light flux within the optical finder 761 by a beam splitter(not shown) and measures the brightness of the object before a pictureis taken.

<Principles>

Seventh Embodiment

An erect real image IM2 of the object OBJ is projected into the fieldmask 765 by the optical finder 761 so that the photographer can verifythe zone of photography by viewing the finder image IM2 through theeyepiece 766.

The state of image formation of the infrared spot image SPT, at the timeof rangefinding, which is a preparation for photography, will now bedescribed.

FIG. 26 is a diagram illustrating the disposition of the infrared spotimage SPT, formed on the main-image sensing device at the time ofrangefinding.

A light-receiving portion 212 of the main image-sensing device 711comprises m₁×n₁ light-receiving pixels and a charge transfer portion(vertical transfer CCD) for transferring electric charge that hasaccumulated in these pixels. A horizontal transfer CCD 213 storeselectric charge transferred in the direction of arrow TRV by thevertical transfer CCD in the light-receiving portion 212, then transfersthe charge in the direction of arrow TRH and outputs an image signalfrom a signal output portion 214 to the image-sensor driver 105.

Further, SPT1 _(T) represents the image of the infrared spot SPT whenthe image-sensing optical system has been set to the maximum telescopicmode, and SPT1 _(W) represents the image of the infrared spot when theimage-sensing optical system has been set to the maximum wide-anglemode. Thus, the size and projected position of the image vary dependingupon the state of the image-sensing optical system.

FIG. 27 illustrates the result of subjecting the image SPT1 _(T) or SPT1_(W) to processing similar to that of the sixth embodiment andnormalizing size and position. The normalized image signal is indicatedat SPT1 ₀. Spacing V_(DEF) between the position of the center of gravityof the signal SPT1 ₀ and a predetermined reference position C isobtained. The distance DST to the object OBJ can be detected inaccordance with Equations (EQ.1) and (EQ.2), in a manner similar to thatof the sixth embodiment, using the reference spacing V₀, the normalizedfocal length f₀ of the image-sensing optical system and baselength BL ofthe optical finder 761. As in the sixth embodiment, information relatingto the reference spacing V₀ conforming to the positions of thefocusing-lens group 152 and zoom-lens group 153 is stored in the ROM ofthe microcomputer 731. Further, f₀ represents the focal length of theimage-sensing optical system normalized by normalization of the size andposition of the spot image. This is an imaginary focal length forobtaining the normalized image signal SPT1 ₀ of FIG. 27 at all timeseven if there is a changed in the zoom state.

The object OBJ is brought into focus automatically if the focusing lensgroup 152 is driven based upon the distance DST to the object OBJcalculated in accordance with Equations (EQ.1), (EQ.2).

FIG. 28 is a diagram showing the camera when the photography switch 122of the camera body 701 is closed upon the completion of the autofocusoperation, thereby establishing the image-sensing state.

When the photography switch 122 is turned on, the light-emitting element724 stops emitting infrared light. The filter actuator 708 is thenactuated to withdraw the infrared passing filter 707 from thephotographic light flux and insert the infrared blocking filter 706 intothe light flux. When this is done, the image IM1 of the object OBJ isformed on the main image-sensing device 711 via the image-sensingoptical system. If FIGS. 25 and 28 are compared, it will be seen thatthe positions of the infrared blocking filter 706 and infrared passingfilter 707 are reversed.

FIG. 29 is a diagram showing the formation of the image of the object onthe main image-sensing device 711 at the time of photography. Theprimary image IM1 of the object OBJ is projected upon theimage-receiving portion 212. Accordingly, the image signal is acquiredunder these conditions and recorded in the image memory 106 of thecamera body 701, whereby the image is sensed.

FIG. 30 is a diagram showing the state of the display on the displayunit 104 after image sensing. The image IM1 acquired in FIG. 29 isdisplayed on the display screen of the display unit 104 as an image IM1_(L) resulting from photography. This allows the photographer todetermine whether photography has been performed correctly.

FIG. 31 is a flowchart showing the control flow of the microcomputer 731when focus detection, focusing, and photography are performed in thecamera body 701 according to the seventh embodiment. The controlflowchart of FIG. 31 will be described with reference to FIGS. 25through 30.

When the main switch 120 of the camera body 701 is turned on, themicrocomputer 731 is activated from the sleep state and control proceedsfrom step S601 to step S602, at which the states of the switches 121-124inside the camera body 701 are sensed.

The state of the photography-preparation switch 121 (SW1), which isturned on by pressing the release button through its first strokelength, is sensed at step S603. Control returns to step S602 when theswitch 121 is off and proceeds to step S604 when the switch 121 is on.

This is followed by step S604, at which the output of theexposure-metering element 768 is read out, object-brightness informationis calculated and, in accordance with a predetermined exposure-controlprogram, a control value for narrowing the stop 155 and the exposuretime (charge storage time) of the image-sensing device 711 arecalculated.

Next, the setting of the AF mode switch 123 is discriminated at stepS605 to determine if the autofocus (AF) mode is in effect. Control jumpsto step S619 if the mode is not the AF mode and proceeds to step S611 ifthe mode is the AF mode.

The microcomputer 731 senses the state of the zoom encoder 165 at stepS611 to judge the current optical status of the lens. It should be notedthat when rangefinding is performed according to this embodiment, thefocusing lens 152 is always at an initial position that corresponds toinfinity. The state of the focus encoder 163, therefore, is not sensed.

A coefficient for making the size of the infrared spot image SPT1conform to the reference value, namely an image-magnification correctioncoefficient, is read out of the ROM (not shown) of microcomputer 731 atstep S612 in the manner described above in connection with FIG. 27.Coefficients are stored in the ROM as matrix data corresponding to thestate of the zoom encoder 165.

Next, the image-position-offset-correction quantity V₀ is read out ofROM at step S613 in the same manner as the image-magnificationcorrection coefficient.

The light-emitting element 724 is activated at step S614 to projectrangefinding infrared light toward the object OBJ.

The main image-sensing device 711 is activated at step S615 to obtainthe signal representing the infrared spot image SPT₁.

Processing of the image signal acquired at step S615 is executed at stepS616. More specifically, the image signal is converted from an analog toa digital quantity.

This is followed by step S617, at which the image size is corrected bymultiplying the image signal of the infrared spot image SPT₁ acquired atstep S616 by the image-magnification correction coefficient read out atstep S612. The resulting signal is converted to the signal SPT10normalized in the manner shown in FIG. 27.

Next, at step S618, the distance DEF to the object is calculated uponcalculating V_(DEF) in accordance with Equations (EQ.1), (EQ.2) usingthe normalized signal SPT10 obtained at step S617 and thepositional-offset correction quantity V₀ obtained at step S613.

The state of the photography switch 122 (SW2) is discriminated at stepS619. If the switch 122 is off, control returns to step S602 so that theprocessing of steps S602-S618, namely the rangefinding operation, isexecuted again. If the photography switch 122 is found to be on at stepS619, it is judged that release has been performed and control shifts tostep S621.

The focusing lens 152 is driven at step S621 based upon the result ofthe calculation at step S618 to bring the image IM1 into focus.

The filter actuator 708 is driven at step S622 to withdraw the infraredpassing filter 707 from the photographic light flux and insert theinfrared blocking filter 706 into the photographic light flux instead.

The stop actuator 166 is driven at step S623 in accordance with thestop-control value calculated at step S604.

Charge accumulation and charge transfer of the main image-sensing devicefor photography are controlled at step S624. This is followed by stepS625, at which processing of the image signal acquired at theabove-mentioned steps is executed. More specifically, the image signalis applied to A/D conversion, white balance adjustment, gamma correctionand compression processing, etc.

Next, at step S626, the signal processed at step S625 is recorded andpreserved in the image memory 106. The image recorded at step S626 isdisplayed on the display unit 104 at step S627, thereby allowing thephotographer to check the image that is the result of photography.

The stop actuator 166 is restored to open the stop 155 at step S628. Theinfrared blocking filter 706 and infrared passing filter 707 areinterchanged, i.e., restored to the positions that prevail at the timeof the rangefinding operation, at step S629. The focusing lens group 152is restored to its initial position at step S630.

Control returns to step S502 when the above-described photographicoperation is completed.

The operation of the camera according to the foregoing flowchart willnow be summarized.

When a switch operation in preparation for photography is performed bythe photographer, infrared light is projected toward the object OBJ fromthe projection module 721 to form the infrared spot SPT on the object,as shown in FIG. 25. As a result, the image-sensing optical system formsthe image of the infrared spot SPT on the main image-sensing device 711via the infrared passing filter 707, and the distance to the object OBJis detected based upon the amount of shift of the spot image from thereference position.

Next, when a picture is taken, the projection of infrared light ishalted and the focusing lens is driven based upon the results ofrangefinding. Next, photography is performed upon changing over thefilter in front of the main image-sensing device 711 to the infraredblocking filter 706, namely to the filter that passes visible light, theimage acquired is stored and preserved in the image memory 106 and theimage of the picture taken is displayed on the display unit 104.

In accordance with the seventh embodiment, the following advantages areobtained in addition to the advantages (AD10)-(AD14) of the sixthembodiment:

(AD15) An active-triangulation-type rangefinding device that projectsinfrared light can be provided. This makes it possible to sense distanceaccurately even in a dark field.

(AD16) Since an infrared spot image is obtained by an image-sensingoptical system having a large aperture, it is possible to measuredistance even to a distant object.

(AD17) Since a changeover is made between an infrared-passing filterused for rangefinding and an infrared-blocking filter used for imaging,rangefinding can be performed without the influence of external lighteven when the field is bright. In addition, degradation of thephotographic image by infrared light can be prevented at the time ofimaging, making it possible to obtain a high-quality image.

(AD18) Since the camera has an optical finder, it is unnecessary topresent an image display by a liquid crystal monitor or the like at thetime of photographic preparations such as rangefinding. This makes itpossible to conserve power.

<Eighth Embodiment>

In the sixth embodiment described above, the image from the mainimage-sensing device 111 is displayed on the display unit 104, such as aliquid crystal monitor, as is when rangefinding is performed. However, aliquid crystal monitor provides a display of low resolution and, thoughit makes it possible to roughly ascertain the focused state, accurateverification of focusing is difficult. In an eighth embodiment describedbelow, a second image of an object is displayed by being superimposed ona first image of the object after being shifted by an amountproportional to the amount of defocusing. In other words, the eighthembodiment provides a finder of double-image coincidence type.

FIGS. 32 through 35 are diagrams relating to the eighth embodiment.

FIG. 32 is a block diagram showing the structure of a camera body 801used in the eighth embodiment. The components are the same as those ofthe sixth embodiment, the only difference being the manner of control atthe time of rangefinding and the manner in which an image is displayed.In the camera body 801 of FIG. 32, the reference numerals 831 and 804 ofthe microcomputer and display unit, respectively, are different fromthose of the sixth embodiment. All other components are the same asthose of the sixth embodiment and operate in the same fashion and neednot be described again.

FIG. 33 corresponds to FIG. 23 of the sixth embodiment and illustrates afirst object image IM31 ₀ for imaging formed in the computation memoryand a second object image IM32DEF within the rangefinding module 621. Inthe sixth embodiment, computation is performed to make the size of thefirst image IM1 of the object conform to the size of the second image ofthe object. According to the eighth embodiment, however, these imagesare used in presenting a display. The second image, therefore, is madeto conform to the first image, which is for image picture-takingpurposes, and it is so arranged that the sizes and limits of the imagesdisplayed on the display unit 804 will coincide with the imaging area.

FIG. 34 is a diagram illustrating the state of a display on the displayunit 804 displaying the image signals of FIG. 33.

An image IM31L from the main image-sensing device 111 is displayed overthe entire display area. A rectangular area AR centered on the displayarea is a twin-image display area in which an image IM32L, which isobtained by extracting part of the image from the subordinateimage-sensing device 624, is displayed in superposition on the imageIM31L. The images IM31L and IM32L are displayed in a form offset fromeach other by an amount DELTA calculated in accordance with thefollowing equation:

DELTA=K·(V _(DEF) −D _(FOCUS))  (EQ.3)

where V_(DEF) represents a quantity relating to the distance to theobject OBJ, D_(FOCUS) represents a quantity relating to the amount offeed of the focusing lens 152 and K represents a coefficient forimproving visibility by enlarging the display-offset quantity.

For example, if we assume that the distance to the object OBJ isinfinity and that the amount of feed of the focusing lens 152 forfocusing the object is zero, then we have

DELTA=K(V _(DEF) −D _(FOCUS))=K·(0−0)=0  (EQ.4)

If the distance to the object is finite, then values of V_(DEF) andD_(FOCUS) conforming thereto are used. However, if the object is infocus owing to the feed of the focusing lens 152, then DELTA =0 holds atthis time as well.

In other words, if the offset quantity DELTA corresponds to the amountof focal shift of the image-sensing system with respect to the objectOBJ and the image IM1 of the object is in focus, then DELTA will alwaysbe equal to zero. Accordingly, a coincidence finder can be implementedby the arrangement described above.

FIG. 35 is a flowchart illustrating the flow of control by themicrocomputer 831 in a case where focus detection, focusing andphotography are carried out in the camera body 801 of the eighthembodiment.

The control flow of FIG. 35 will be described while making reference toFIGS. 32 and 34.

When the main switch 120 of the camera body 801 is turned on, themicrocomputer 831 is activated from the sleep state and control proceedsfrom step S701 to step S702, at which the states of the switches 121-124inside the camera body 801 are sensed.

The state of the photography-preparation switch 121 (SW1), which isturned on by pressing the release button through its first strokelength, is sensed at step S703. Control returns to step S702 when theswitch 121 is off and proceeds to step S704 when the switch 121 is on.

Next, at step S704, the main image-sensing device 111 is activated toacquire an image signal.

Processing of the image signal acquired at step S704 is executed at stepS705. More specifically, processing such as A/D conversion of the imagesignal, white balance adjustment and gamma correction is executed.

This is followed by step S706, at which object-brightness information iscalculated from the image signal processed at step S705. Further, inaccordance with a predetermined exposure-control program, a controlvalue for stopping down the stop 155 and the exposure time (chargestorage time) of the image-sensing device 111 are calculated.

Next, the setting of the AF mode switch 123 is discriminated at stepS707 to determine if the autofocus (AF) mode is in effect. Control jumpsto step S722 if the mode is not the AF mode and proceeds to step S711 ifthe mode is the AF mode.

The microcomputer 831 senses the state of the focus encoder 163 at stepS711 and senses the state of the zoom encoder 165 at step S712 to judgethe current optical status of the lens.

A coefficient for making the size of the first image IM1 of the objectequal to that the second image of the object, namely an imagemagnification correction coefficient, is read out of the ROM ofmicrocomputer 831 at step S713 in the manner described above inconnection with FIGS. 22A, 22B. Coefficients are stored in the ROM asmatrix data corresponding to the states of the focus encoder 163 andzoom encoder 165.

Next, a position-offset-correction quantity V₀ is read out of the ROM atstep S714 in the same manner as the image-magnification correctioncoefficient.

The subordinate image sensing device 624 is activated at step S715 toobtain an image signal.

Processing of the image signal acquired at step S715 is executed at stepS716. More specifically, processing such as A/D conversion of the imagesignal, white balance adjustment and gamma correction is executed.

This is followed by step S717, at which the image size is corrected bymultiplying the image signal of the second image IM2 acquired at stepS715 by the reciprocal of the image-magnification correction coefficientread out at step S713.

Next, at step S718, the distance to the object is calculated inaccordance with Equations (EQ.1), (EQ.2) using the second image IM2 thatwas subjected to the image-magnification correction at step S717, thefirst image IM1 obtained at step S705 and the position-offset-correctionquantity V₀ obtained at step S714.

The focusing-lens group 152 is driven at step S719 based upon the resultof the above-described calculation to bring the first image IM1 intofocus.

This is followed by step S720, at which the offset DELTA between the twoimages for display shown in FIG. 34 is calculated in accordance withEquation (EQ.3) and processing for superposing the two images isexecuted.

Next, at step S721, the image signal obtained at step S720, namely thesplit-image coincidence image signal, is displayed on the display unit804.

The state of the photography switch 122 (SW2) is discriminated at stepS722. If the switch 122 is off, control returns to step S702 so that theprocessing of steps S702-S721 is executed again. If the photographyswitch 122 is found to be on at step S722, it is judged that release hasbeen performed and control shifts to step S731.

Steps S731-S736 are for an image-sensing operation identical with thatof steps S521-S526 of FIG. 24 according to the sixth embodiment. Whenthe processing of step S736 is completed, control returns to step S702.

The operation of the camera according to the foregoing flowchart willnow be summarized.

When the main switch 120 and photography-preparation -switch 121 areturned on by the photographer, the camera performs the rangefindingcalculation and carries out autofocusing by driving the focusing lens ina manner similar to that of the sixth embodiment. On the basis of theresults of rangefinding calculation and the results of driving thefocusing lens, the state of focusing of the object is displayed as theamount of shift between two images on the double-image coincidencedisplay device. Continuous focusing is performed by repeatedly executingthis operation and the photographer is notified of the results offocusing in the form of the amount of offset between the twin images.Next, when the photography switch 122 is turned on, the image of theobject projected upon the main image-sensing device is recorded in theimage memory and an image of the picture taken is displayed on thedisplay unit 804.

The eighth embodiment provides the following advantage in addition tothe advantages (AD10)-(AD14) according to the sixth embodiment.

(AD19) The state of focusing is displayed as a coincidence finder imageon an electronic finder such as a liquid crystal monitor. As a result,the status of focus of the image of the object is made much morediscernible.

<Ninth Embodiment>

According to the eighth embodiment, a photoelectric coincidence finderis realized using the rangefinding device of the sixth embodiment. Aninth embodiment described below illustrates a case where thephotoelectric coincidence finder is realized using the conventionalpassive- or active-type rangefinding device.

FIGS. 36 through 39 are diagrams relating to the ninth embodiment.

FIG. 36 is a diagram showing the construction of a camera body 901according to the ninth embodiment. Components other than those describedbelow operate in the same manner as set forth in connection with thesixth embodiment of FIG. 20. Only the components that differ will bedescribed.

The camera body 901 has various functional components for forming theimage of an object OBJ, detecting focus, and sensing the image.

A rangefinding module 921 has two light-receiving lenses 922 of the samepower spaced apart by a predetermined baselength BL for forming imagesIM2, IM3 of the object OBJ whose distance is to be measured, aninfrared-blocking filter 923 for blocking infrared light and passingonly visible light of the light flux that has passed through thelight-receiving lens 922, and a subordinate image-sensing device 924.The rangefinding optical system, which includes the light-receivinglenses 922 and the infrared-blocking filter 923, forms a second imageIM2 of the object OBJ and a third image IM3 of the object OBJ on thesubordinate image-sensing device 924, described later.

The subordinate image-sensing device 924, such as a CCD, is atwo-dimensional photoelectric sensor for photoelectrically convertingthe second and third images IM2, IM3 of the object. The distance to theobject OBJ can be detected from the spacing between images IM2, IM3 andthe baselength BL using a prescribed calculation formula.

A microcomputer 431 performs rangefinding and presents a display on acoincidence finder in accordance with a flowchart described below.

FIG. 37 is a diagram showing the subordinate image-sensing device 924and the disposition of two images formed on the image-sensing device.

A light-receiving portion 925 of the subordinate image-sensing device924 comprises m₂×n₂ light-receiving pixels and a charge transfer portion(vertical transfer CCD) for transferring electric charge that hasaccumulated in these pixels. A horizontal transfer CCD 926 storeselectric charge transferred in the direction of arrow TRV by thevertical transfer CCD in the light-receiving portion 925, then transfersthe charge in the direction of arrow TRH and outputs an image signalfrom an signal-output portion 927 to the image sensor driver 134.

The second and third images of the object described in connection withFIG. 36 are shown at IM2 and IM3, respectively, and the spacing V_(DEF)between the two images varies depending upon the object to the distanceOBJ.

In accordance with a well-known correlation algorithm, the distanceV_(DEF) Of the image IM3 relative from the image IM1 is obtained anddistance DST to the object OBJ can be detected based upon the followingequation using the focal length f of the light-receiving lens 922 andbaselength BL: $\begin{matrix}{{DST} = \frac{f \cdot {BL}}{\left( {V_{DEF} - {BL}} \right)}} & \left( {{EQ}.\quad 5} \right)\end{matrix}$

FIG. 38 is a diagram illustrating the form of the display presented on adisplay unit 904. An image IM1L₀ from the main image-sensing device 111is displayed over the entire display area. A rectangular area ARcentered on the display area is a twin-image display area. An imageIM1L_(DEF), which is obtained by extracting the central portion of animage which is the copy of the image IM1L₀ obtained by the image sensingdevice 111, is displayed in the area AR in superposition on the imageIM1L₀. The images IM1L₀ and IM1L_(DEF) are displayed in a form offsetfrom each other by an amount DELTA calculated in accordance with thefollowing equation:

DELTA=K×(V _(DEF) −D _(FOCUS))  (EQ. 6)

where V_(DEF) represents a quantity relating to the distance to theobject OBJ, D_(FOCUS) represents a quantity relating to the amount offeed of the focusing lens 152 and K represents a coefficient forimproving visibility by enlarging the display offset quantity.

For example, if we assume that the distance to the object OBJ isinfinity and that the amount of feed of the focusing lens 152 forfocusing the object is zero, then the display image-offset quantityDELTA will be represented by the following equation, which is similar toEquation (EQ.4) of the eighth embodiment:

DELTA=K×(V _(DEF) −D _(FOCUS))=K×(0−0)=0  (EQ. 7)

If the distance to the object is finite, then values of V_(DEF) andD_(FOCUS) conforming thereto are used. However, if the object is infocus owing to feed of the focusing lens 152, then DELTA=0 holds at thistime as well.

In other words, according to the ninth embodiment, the construction ofthe rangefinding module 921 and the images superposed on each other inthe twin-image display area of the display unit 904 differ from those ofthe eighth embodiment. However, as in the eighth embodiment, the offsetquantity DELTA corresponds to the amount of focal shift of theimage-sensing system with respect to the object OBJ, and a finder oftwin-image coincidence type similar to that of the eighth embodiment canbe implemented.

FIG. 39 is a flowchart illustrating the flow of control by themicrocomputer 931 in a case where focus detection, focusing andphotography are carried out in the camera body 901 of the ninthembodiment.

The control flow of FIG. 39 will be described while making reference toFIGS. 36 through 38.

When the main switch 120 of the camera body 901 is turned on, themicrocomputer 931 is activated from the sleep state and control proceedsfrom step S801 to step S802, at which the states of the switches 121 -124 inside the camera body 901 are sensed.

The state of the photography-preparation switch 121 (SW1), which isturned on by pressing the release button through its first strokelength, is sensed at step S803. Control returns to step S802 when theswitch 121 is off and proceeds to step S804 when the switch 121 is on.

Next, at step S804, the main image sensing device 111 is activated toacquire an image signal.

Processing of the image-signal acquired at step S804 is executed at stepS805. More specifically, processing such as A/D conversion of the imagesignal, white-balance adjustment, and gamma correction is executed.

This is followed by step S806, at which object-brightness information iscalculated from the image signal processed at step S805. Further, inaccordance with a predetermined exposure-control program, a controlvalue for stopping down the stop 155 and the exposure time (chargestorage time) of the image sensing device 111 are calculated.

Next, the setting of the AF mode switch 123 is discriminated at stepS807 to determine if the autofocus (AF) mode is in effect. Control jumpsto step S820 if the mode is not the AF mode and proceeds to step S811 ifthe mode is the AF mode.

The microcomputer 931 senses the state of the focus encoder 163 at stepS811 and senses the state of the zoom encoder 165 at step S812 to judgethe current optical status of the lens. The subordinate image sensingdevice 924 is activated at step S813 to obtain image signals forrangefinding purposes.

Next, the image signals acquired at step S813 are subjected toprocessing such as A/D conversion at step S814. Next, at step S815, theposition offset quantity between the digital image signals of the imagesIM2 and IM3 obtained at step S814 is calculated and so is the distanceto the object.

The focusing lens group 152 is driven at step S816 based upon the resultof the above-described calculation to bring the first image IM1 intofocus.

The offset quantity DELTA between the two images for display purposesshown in FIG. 38 is calculated in accordance with Equation (EQ.6) atstep S817.

This is followed by step S818, at which processing for superposing thetwo images in the manner shown in FIG. 38 is executed.

Next, at step S819, the image signal obtained at step S818, namely thesplit-image coincidence image signal, is displayed on the display unit904.

The state of the photography switch 122 (SW2) is discriminated at stepS820. If the switch 122 is off, control returns to step S802 so that theprocessing of steps S802-S819, namely automatic focusing and display ofimages on the display unit, is executed again. If the photography switch122 is found to be on at step S820, it is judged that release has beenperformed and control shifts to step S831.

Steps S831-S836 are for an image-sensing operation identical with thatof steps S731-S736 of FIG. 35 according to the eighth embodiment. Whenthe processing of step S836 is completed, control returns to step S702.

The operation of the camera according to the foregoing flowchart willnow be summarized.

When the main switch 120 and photography-preparation switch 121 areturned on by the photographer, the camera performs the rangefindingcalculation using the image signals obtained from the rangefindingmodule 921 and carries out automatic focusing by driving the focusinglens 152 based upon the results of rangefinding calculation. On thebasis of the results of rangefinding calculation and the results ofdriving the focusing lens, the state of focal shift of the image on theimage sensing device 111 is calculated. The image of the object obtainedfrom the image-sensing device 111 and an image obtained by extractingthe central portion of an image, which is a copy of the first-mentionedimage, are superposed and displayed on the display unit 904 with anoffset between them that depends upon the amount of focal shift.Continuous focusing is performed by repeatedly executing this operationand the photographer is notified of the results of focusing in the formof the amount of offset between the twin images. Next, when thephotography switch 122 is turned on, the image of the object projectedupon the main image-sensing device is recorded in the image memory andimage of the picture taken is displayed on the display unit 904.

The ninth embodiment provides the following advantage in addition to theadvantages (AD10)-(AD14) according to the sixth embodiment.

(AD20) The state of focusing is displayed as a coincidence finder imageeven in an image-sensing apparatus having the conventional rangefindingdevice and an electronic finder, such as a liquid crystal monitor. As aresult, the status of focus of the image of the object is made much morediscernible through a simple, inexpensive arrangement.

The rangefinding device in the ninth embodiment uses a passivetriangulation rangefinder according to the prior art. However, it ispossible to use a conventional active triangulation rangefinding deviceor a so-called sonar-type rangefinding device, which measures distancebased upon the length of time required to receive reflected ultrasonicwaves projected toward an object.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. An apparatus comprising: a light reception devicereceiving light from an object and generating light reception signalsthereof; a phase difference determination device determining a phasedifference between two light reception signals, generated by said lightreception device, respectively corresponding to two light rays indifferent directions emitted from a part of the object; and a displaydevice selecting one reception signal of the two light reception signalsto display an image of the object on the basis of the selected onereception signal.
 2. An apparatus according to claim 1, furthercomprising a focus adjustment device adjusting an image forming opticalsystem on the basis of a determination result of said phase differencedetermination device.
 3. An apparatus according to claim 1, furthercomprising an optical device guiding the two light rays emitted from thepart of the object to respective different light reception positions ofsaid light reception device.
 4. An apparatus according to claim 3,wherein when said optical device guides the two light rays emitted fromthe part of the object to the respective different light receptionpositions, said display device selects the one light reception signal ofthe two light reception signals to display the image of the object onthe basis of the selected light reception signal, and wherein when saidoptical device does not operate, said display device displays an imageof the object on the basis of the light reception signal of said lightreception device without performing a selection of the one lightreception signal.
 5. An apparatus according to claim 4, wherein saiddisplay device displays the images of the object so that a magnificationfactor of the object images are the same for when the selection of thelight reception signal is made and when the selection of the lightreception signal is not made.
 6. An apparatus according to claim 1,wherein said apparatus comprises an optical apparatus.
 7. An apparatusaccording to claim 1, wherein said apparatus comprises a camera.
 8. Acontrol method comprising the steps of: receiving light from an objectby a light reception device and obtaining light reception signalsthereof; determining a phase difference between two light receptionsignals, obtained by the light reception device, respectivelycorresponding to two light rays in different directions emitted from apart of an object; and selecting one light reception signal of the twolight reception signals to display an image of the object on the basisof the selected one light reception signal.
 9. A method according toclaim 8, further comprising a step of adjusting a focus of an imageforming optical system on the basis of a determination result of saidphase difference determining step.
 10. A method according to claim 8,further comprising a step of displaying the one light reception signalselected in said selection step, when the two light rays emitted fromthe part of the object are guided to respective different lightreception positions of the light reception device by an optical device,and a step of displaying, when the optical device does not operate, animage of the object on the basis of the light reception signal of thelight reception device without performing a selection of the one lightreception signal.
 11. A method according to claim 10, further comprisinga step of displaying the images of the object so that magnificationfactors of the object images are the same for when the selection of thelight reception signals is made and when the selection of the lightreception signals is not made.
 12. A computer readable storage mediumcontaining a computer readable program comprising code for instructing acomputer to perform the steps of: receiving light from an object by alight reception device and obtaining light reception signals thereof;determining a phase difference between two light reception signals,obtained by the light reception device, respectively corresponding totwo light rays in different directions emitted from a part of an object;and selecting one light reception signal of the two light receptionsignals to display an image of the object on the basis of the selectedone light reception signal.
 13. A computer-readable storage mediumaccording to claim 12, said computer-readable program further comprisingcode for instructing the computer to perform a step of: adjusting afocus of an image forming optical system on the basis of a determinationresult of said phase difference determination step.
 14. Acomputer-readable storage medium according to claim 12, said computerreadable program further comprising code for instructing the computer toperform steps of: displaying the one light reception signal selected insaid selection step, when the two light rays emitted from the part ofthe object are guided to respective different light reception positionsof the light reception device by an optical device, and displaying, whenthe optical device does not operate, an image of the object on the basisof the light reception signal of the light reception device withoutperforming a selection of the one light reception signal.
 15. Acomputer-readable storage medium according to claim 14, said computerreadable program further comprising code for instructing the computer toperform a step of: displaying the images of the object so thatmagnification factors of the object images are the same for when theselection of the light reception signals is made and when the selectionof the light reception signals is not made.
 16. An apparatus comprising:a light reception device receiving light from an object and generatinglight reception signals thereof; a phase difference determination devicedetermining a phase difference between two light reception signals,generated by said light reception device, respectively corresponding totwo light rays in different directions emitted from a part of theobject; and a display device displaying an image of the object on thebasis of the light reception signals generated by said light receptiondevice.
 17. An apparatus according to claim 16, wherein said displaydevice displays the image that corresponds to one reception signal ofthe two light reception signals.
 18. An apparatus according to claim 16,further comprising a focus adjustment device adjusting an image formingoptical system on the basis of a determination result of said phasedifference determination device.
 19. An apparatus according to claim 16,further comprising an optical device guiding the two light rays emittedfrom the part of the object to respective different light receptionpositions of said light reception device.
 20. An apparatus according toclaim 16, wherein said apparatus comprises an optical apparatus.
 21. Anapparatus according to claim 16, wherein said apparatus comprises acamera.
 22. A control method comprising the steps of: receiving lightfrom an object by a light reception device and obtaining light receptionsignals thereof; determining a phase difference between two lightreception signals, obtained by said light reception device, respectivelycorresponding to two light rays in different directions emitted from apart of the object; and displaying an image of the object on the basisof the light reception signals obtained by said light reception device.23. A control method according to claim 22, wherein said displaying stepdisplays the image that corresponds to one reception signal of the twolight reception signals.
 24. A control method according to claim 22,further comprising a step of adjusting an image forming optical systemon the basis of a determination result of said determining step.
 25. Acontrol method according to claim 22, further comprising a step ofguiding the two light rays emitted from the part of the object torespective different light reception position of the light receptiondevice.
 26. A computer program product comprising code for instructing acomputer to perform the steps comprising: receiving light from an objectby a light reception device and obtaining light reception signalsthereof; determining a phase difference between two light receptionsignals, obtained by the light reception device, respectivelycorresponding to two light rays in different directions emitted from apart of the object; and displaying an image of the object on the basisof the light reception signals obtained by the light reception device.27. A computer program product according to claim 26, wherein saiddisplaying step displays the image that corresponds to one receptionsignal of the two light reception signals.
 28. A computer programproduct according to claim 26, further comprising adjusting an imageforming optical system on the basis of a determination result of saiddetermining step.
 29. A computer program product according to claim 26,further comprising guiding the two light rays emitted from the part ofthe object to respective different light reception positions of thelight reception device.